The WEX legal dictionary says:
In both tort and criminal law, strict liability exists when a defendant is liable for committing an action, regardless of what his/her intent or mental state was when committing the action. In criminal law, possession crimes and statutory rape are both examples of strict liability offenses.
It goes on to say:
In criminal law, strict liability is generally limited to minor offenses. Criminal law classifies strict liability as one of five possible mentes reae (mental states) that a defendant may have in pursuit of the crime. The other four are "acting knowingly," "acting purposely," "acting with recklessness," and "acting with negligence." The mens rea of strict liability typically results in more lenient punishments than the other four mentes reae. Typically in criminal law, the defendant's awareness of what he is doing would not negate a strict liability mens rea (for example, being in possession of drugs will typically result in criminal liability, regardless of whether the defendant knows that he is in possession of the drugs)
In tort law, there are two broad categories of activities for which a plaintiff may be held strictly liable - possession of certain animals and abnormally dangerous activities. Additionally, in the area of torts known as products liability, there is a sub-category known as strict products liability which applies when a defective product for which an appropriate defendant holds responsibility causes injury to an appropriate plaintiff.
In a linked article, Wex says:
A person who is found by a court to have carried on an abnormally dangerous activity will be subject to strict liability for physical harm resulting from that activity. See Restatement (Third) of Torts. § 20(a) (2009).
Courts have often identified blasting (the controlled use of explosives to break down or remove rocks) as the paradigm of an abnormally dangerous activity because of its inherent dangers, and they applied strict liability in cases where blasting resulted in physical harm.
an activity that is generally safe when all participants exercise reasonable care is not an abnormally dangerous activity. To be deemed abnormally dangerous, any activity must present a highly significant risk of physical harm even when all participants are reasonably careful. Most ordinary activities can be made generally safe through the exercise of reasonable care, and thus fall under the rule of negligence liability (as opposed to strict liability). See Restatement (Third) of Torts § 20, cmt.(h) (2009).
The Wikipedia article says:
In criminal and civil law, strict liability is a standard of liability under which a person is legally responsible for the consequences flowing from an activity even in the absence of fault or criminal intent on the part of the defendant.
In the field of torts, prominent examples of strict liability may include product liability, abnormally dangerous activities (e.g., blasting), intrusion onto another's land by livestock, and ownership of wild animals. Traditional criminal offenses which require no element of intent (mens rea) include statutory rape and felony murder.
In tort law, strict liability is the imposition of liability on a party without a finding of fault (such as negligence or tortious intent). The claimant need only prove that the tort occurred and that the defendant was responsible. The law imputes strict liability to situations it considers to be inherently dangerous.
The doctrine's most famous advocates were Learned Hand, Benjamin Cardozo, and Roger J. Traynor.
Strict liability is sometimes distinguished from absolute liability. In this context, an actus reus (guilty act) may be excused from strict liability if due diligence is proved. Absolute liability, however, requires only an actus reus.
In the United States strict liability can be determined by looking at the intent of the legislature. If the legislature seems to have purposefully left out a mental state element (mens rea) because they felt mental state need not be proven, it is treated as a strict liability.
The Justia article says:
Strict liability is a theory that imposes legal responsibility for damages or injuries even if the person who was found strictly liable did not act with fault or negligence. This theory usually applies in three types of situations: animal bites (in certain states), manufacturing defects, and abnormally dangerous activities.
Most states now impose strict tort liability for defectively manufactured products. Plaintiffs in states that recognize strict liability for manufacturing defects will not need to show that the manufacturer failed to use due care or was reckless. A plaintiff can recover damages even if the manufacturer used all appropriate care in the preparation of the product.
A plaintiff suing under a theory of strict liability will need to show that there was a defect, that the defect actually and proximately caused the plaintiff’s injury, and that the defect made the product unreasonably dangerous. Not only buyers of the product, but also bystanders or guests and others who do not have a direct relationship with the product can sue for strict liability if they are injured by the product.
The Nolo article says:
“Strict liability” is a concept mainly applicable to civil, rather than criminal, law. It’s a way of holding someone accountable for behavior regardless of fault. It often arises with lawsuits against product manufacturers—in applicable cases, the plaintiff doesn’t need to show that the manufacturer was negligent in creating the product.
In criminal law, strict liability laws punish people regardless of their state of mind—the prosecution doesn’t need to prove that a defendant intended to do something that's illegal. The prosecution doesn’t even need to establish that the defendant was reckless or negligent.
The most common example of a strict liability crime is statutory rape: In many states, it’s a crime to have sex with a minor, no matter the circumstances. It’s a crime in those places even if the defendant honestly and reasonably believed that the sexual partner was old enough to give legal consent.
In Foster v. Preston Mill Co. 44 Wn.2d 440 (1954) The Supreme Court of Washington wrote:
The modern doctrine of strict liability for dangerous substances and activities stems from Justice Blackburn's decision in *Rylands v. Fletcher**, 1 Exch. 265, decided in 1866 and affirmed two years later in Fletcher v. Rylands, L.R. 3 H.L. 330. Prosser on Torts, 449, § 59. As applied to blasting operations, the doctrine has quite uniformly been held to establish liability, irrespective of negligence, for property damage sustained as a result of casting rocks or other debris on adjoining or neighboring premises. Patrick v. Smith, 75 Wash. 407, 134 Pac. 1076; Schade Brewing Co. v. Chicago, M. & P.S.R. Co., 79 Wash. 651, 140 Pac. 897; Bedell v. Goulter, 199 Ore. 344, 261 P. (2d) 842; Exner v. Sherman Power Constr. Co., 54 F. (2d) 510. But, see Klepsch v. Donald, 4 Wash. 436, 30 Pac. 991.
There is a division of judicial opinion as to whether the doctrine of absolute liability should apply where the damage from blasting is caused, not by the casting of rocks and debris, but by concussion, vibration, or jarring. This court has adopted the view that the doctrine applies in such cases. See Patrick v. Smith, supra. In the Patrick case, it was held that contractors who set off an exceedingly large blast of powder, causing the earth for a considerable distance to shake violently, were liable to an adjoining owner whose well was damaged and water supply lost, without regard to their negligence in setting off the blast, although there was no physical invasion of the property. For excellent expositions of this view, see Exner v. Sherman Power Constr. Co., supra; and Bedell v. Goulter, supra.
In his article Strict Liability in Negligence published in the DePaul Law Review (2012) Kenneth S. Abraham, writes:
The distinction between strict liability and negligence is a fundamental feature of tort law. Tort law theory contrasts strict liability and negligence by identifying different justifications for each standard.'Tort law in practice draws a sharp distinction between strict liability and negligence. Not only is this distinction highly important as a matter of substance; it seems to be taken for granted that the distinction is clear and uncontroversial
What actually amounts to strict liability in negligence is virtually never labeled this way in the case law. But saying that strict liability is negligence does not make it so. ... I am less concerned with terminology here than with the fact that, whatever these forms of liability may be called, they are distinctive in certain ways from much of mainstream negligence and are therefore worthy of separate attention.
A negligence system that purports to condition liability on the commission of wrongs-but also sometimes imposes stricter liability for conduct that is not so clearly blameworthy-would seem to be influenced in practice by the same instrumental considerations that support the imposition of strict liability.
Negligence is the failure to exercise reasonable care; strict liability is the imposition of liability even when reasonable care has been exercised.
there are forms of liability that are imposed without regard to negligence and that carry little or no disapproval. For most commentators, "traditional" strict liability for harm caused by abnormally dangerous activities falls into this category. There is no message implied in the imposition of this form of liability that the defendant should have behaved differently. Such conduct does not breach a standard of care.
The Newsome-Melton article "Negligence And Strict Liability" says:
The two most common causes of action alleged, and by far the two most common to be tried are strict liability and negligence. Each requires proof of different elements and, despite their similarities, one theory or the other will typically prove more likely to result in judgment in any particular case.
The elements of a cause of action for negligence are:
(1) A duty of care owed by the defendant to the user of a product or a foreseeable bystander.
(2) Breach of that duty, meaning that the defendant’s conduct falls below the applicable standard of care for the activity in which he is engaged.
(3) Injury to the plaintiff that was caused by the breach.
The doctrine of strict liability is most succinctly stated in the RESTATEMENT (SECOND) OF TORTS §402A (American Law Institute 1965):
(1) One who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his property is subject to liability for physical harm thereby caused to the ultimate user or consume, or to his property, if
(a) the seller is engaged in the business of selling such a product, and
(b) it is expected to and does reach the user or consumer without substantial change in the condition in which it is sold.
(2) The rule stated in Subsection (1) applies although
(a) the seller has used all possible care in the preparation and sale of the product, and
(b) the user or consumer has not bought the product from or entered into any contractual relation with the seller.
Subsections (2)(a) and (b) obviously distinguish strict liability as a cause of action completely separate from negligence and breach of warranty actions
In short, there are criminal laws which impose penalties and allow people to be found guilty with no evidence of any guilty intent or even negligent action. And there are kinds of cases in which tort liability may be found in the absence of negligence or intent, even if the defendant took all reasonable precautions. These kinds of cases are limited, but within these limits proof of intent or negligence is simply not required.