Dale M. has a pretty good, black letter law definition: "Entrapment involves the law enforcement officer inducing the perpetrator to commit a crime that they otherwise would not." However, I think that from a practical standpoint I'd actually go even further: A defense on the basis of entrapment is highly unlikely to succeed unless the law enforcement officer puts the idea to commit the crime in your head and then persuades you to do it. Or, to use a couple of (only slightly facetious) hypotheticals:
Undercover law enforcement officer says to you: "Man, I could really use some cash. You know, we could rob a bank."
You: "Huh, well, I think ABC Bank has pretty lousy security guards. We could hit that one, if we wanted to. Yeah, that's a pretty good idea."
Undercover: "Hey, that sounds like a plan to me. I'm in if you are."
You: "Yeah, I think I am. Let's do it."
Undercover: "Man, we could both use some cash. Why don't we rob a bank or something?"
You: "I don't know. That sounds kinda dangerous. Plus, if we get caught we could go to a federal prison for years. I don't think I'd be down with that."
Undercover: "Oh, come on. I know this sweet bank, ABC Bank. Terrible security. We'd be in and out in no time. No danger, nobody goes to prison. And you need cash as bad as I do, don't you?"
You: "Well, yeah, I guess so."
Undercover: "Alright, so don't be chicken. Let's do it."
Undercover: "Oh, come on. Easy money!!"
You: "Okay, I guess."
Let's put it this way: When I took criminal procedure in law school the modern cases we read all had the same theme: "No, X doesn't constitute entrapment." To my knowledge, it's just a really, really hard defense to win on in modern American law. (Under federal law and in almost all states, as far as I'm aware.)
Requisite disclaimer: I am not a criminal lawyer who has direct experience with making entrapment law defenses under the law of whatever jurisdiction you might be worried about potentially being charged under. If you want a definitive, reliable answer you need to talk to somebody who is. (You already figured that out, I'm sure, but just for the record...) Still, maybe this helps.