Mea culpa, which means "through my fault" in Latin, comes from a prayer of confession in the Catholic Church. Said by itself, it's an exclamation of apology or remorse that is used to mean "It was my fault" or "I apologize." Mea culpa is also a noun, however.

How do you use the phrase mea culpa?

It literally means “through my (own) fault.” Mea culpa can be used as an interjection (much like my fault or my bad) or as a noun referring to an apology, as in The senator offered a mea culpa during the press conference. Example: Dave usually has a hard time admitting he's wrong, so his mea culpa means a lot.

Who first said mea culpa?

Geoffrey Chaucer's 14th-century Troilus and Criseyde uses it in a way that shows it was already a traditional religious phrase: "Now, mea culpa, lord! I me repente."