The name commonly applied to the symbol in logic. ⊥, when used as a "logical constant", i.e. a zero argument predicate, not as a relation!

⊥ stands for your favourite contradiction. For example, in a propositional calculus, ⊥ might stand for "P&~P" for some proposition P. The truth value of ⊥ is therefore obviously "false". This gives rise both to symbol and name: it's an upside down "T", so it's pronounced "eet", á la "atled".

Chiefly seen with people who deal with Robinson resolution and various related proof systems.