When an author invents a new term such as Mithril or Orc in Lord of The Rings or Redstone in Minecraft, are there restrictions on the use of those terms?
If I write my own book or create a video game would it be an infringement to use Mithril or Redstone as a fictitious item?
If so what are those limitations? If my redstone was actually a blue liquid that explodes instead of a red powder that conducts electricity would that be different?
Copyright law does not protect names, titles, or short phrases or expressions. Even if a name, title, or short phrase is novel or distinctive or lends itself to a play on words, it cannot be protected by copyright.
The only intellectual property protection that might be afforded to such things is trademark.
The previous answer that short phrases, including individual words, names, or titles, cannot be copyrighted, is correct. However, if a work uses many unique names from the same source, that might be evidence tending to establish that it is a derivative work and thus subject to the copyright on the source work (if that is still protected).
By the way, unlike "mithril" the word "orc" was not coined by Tolkien. It appears in Beowulf, which of course JRRT knew very well indeed.
Expanding upon the other answers, if an entire vocabulary or set of concepts or the characteristic features of a work are shared by multiple authors in a common genre to the point that they becomes genre conventions, their use on a work is not copyright infringing due to the Scène à faire doctrine.
"Mithril" is used as a metal name in the Runescape online game, apparently without legal challenge. It's blue in the game rather than silvery as in the Tolkien books.
On the other hand, Tactical Studies Rules (later TSR Inc.) was forced to change "hobbit" to "halfling" and "ent" to "treant" between printings of the original Dungeons and Dragons, probably because they used "hobbit" and "ent" to mean the same things Tolkien did. They continued using "orc", since that word wasn't created by Tolkien, although D&D orcs were obviously based on Tolkien.
"Redstone", as a word, is older than Minecraft. Alan Shepard was launched into space on a Redstone rocket.
