Another word for a pacifier, comforter or security blanket, but it can be used as a metaphor. Originating from the comic strip Peanuts, the character Linus is always holding his blanket for protection. His dependence has lead to this being a pop-culture reference to all such objects in relation to those who need them.
The term became a lot more popular after the term was used by Simon Pegg in an early episode of the hit TV sitcom Spaced.
"Does the convenience storekeeper really need that Baseball bat under the counter?"
"Not really, it's just a Linus Blanket, he'll never use it!"