...and our word for today is "Closure" (JavaScript)

"A closure is an expression (typically a function) that can have free variables together with an environment that binds those variables (that "closes" the expression)."

A very enlightening use and abuse article on the topic by Richard Cornford. March 2004.
It's enlightening because it involves key concepts in JavaScript related to object orientation, scope, and identifier resolution. These things are almost always not understood by casual JavaScript hackers (speaking from past experience).