From Looney Labs' Webstore:
This New Rule card works in any Fluxx deck.
It says, "Any time a numeral is seen on another card, add one to that numeral. For example, 1 becomes 2, while one remains one. This does affect the Basic Rules."
This card was originally released as part of a trio of promo cards for Origins 2002. It was originally entitled simply "X=X+1". It was then subsequently incorporated into the main game, with the release of Fluxx 3.0.
The switch to version 3.1 saw the name changed to "Inflation" as "X=X+1" was deemed too cryptic and programmer-oriented for the general population. The art still features the iconic phrase.
As it proved to be a "love it or hate it" kind of card, it was never included in any other versions of Fluxx besides the original game (although it did make the cut for inclusion in version 4.0).
It was reprinted as a promo card with the "Inflation" title in the summer of 2010 so that fans who loved it could buy it singly to add to any of their other Fluxx decks. Enjoy!