The triple bar, ≡, is a symbol used in formal logic. It has the appearance of a "=" sign with a third line.
Logically, it has a similar meaning to the if and only if coupler ⇔. However, in some texts ⇔ is used as a symbol in logic formulas, while ≡ is for reasoning about those formulas (as in metalogic).
It is Unicode character 8801. The HTML entity ≡ also corresponds to the triple bar.
