The Absolute Value Card (AVC) is a function within a card; it causes some numerical value to be viewed as positive (or negative, with proper care) regardless of its sign (hence why it is named after the similar mathematics operation). While not incredibly important, this card archetype crops up in enough decks that it deserves its own entry.
There are a few forms that an AVC shows up in, and their usage can often vary.
The classical form is when you write down "+|1000| points!" to make sure that Munchkin Billy can't make all point values negative so that he wins with a perfect 0 on his score. This can also be used to re-enforce the threat of a mega point card.