[njohnson41]

I think one of the common terms for this is a "motte and bailey doctrine", where people define their terms one way during an argument to make their statements super-defensible, but later redefine them to mean whatever crazy thing they actually meant. People seem to use this intentionally and unintentionally a lot.

http://slatestarcodex.com/2014/11/03/all-in-all-another-bric...