The Latin expression mea culpa is used as an interjection and as a noun.
mea culpa interjection: an exclamation acknowledging one’s guilt or responsibility for an error. For example:
MOTHER: The garbage is overflowing!
SON: Mea culpa! I’ll take it out right now.
As a noun, a mea culpa is the acknowledgement of one’s guilt or responsibility for an error and is often used as a synonym for apology.
Here are examples of this use:
Just before Guillen began his 45-minute mea culpa…the Marlins announced he had been suspended for five games.
Anthony Weiner’s emotional mea culpa: Will it be enough?
Does McCain owe mea culpa to POWs & MIAs?
Hydro owes us a mea culpa.
An apology is “an acknowledgement of an offense with expression of regret for it, by way of reparation.”
Mea culpa as a synonym for apology derives from its use in a Latin prayer called “The Confiteor.” The Latin word confiteor means, “I confess” or “I acknowledge.” In praying, the supplicant repeats the phrase mea culpa, “through my own fault,” numerous times during the recitation of the prayer.
An error with mea culpa occurs when a writer doesn’t understand its English meaning. Here are examples of misuse:
Annie gritted her teeth and lifted her hands briefly from the wheel in a mea culpa apology to the indignant driver of the cleaner’s van.—Novel published by Random House.
Rather than from John Paul Culotta, The Progressive, a mea culpa apology is due from the cretins who faithfully followed our “torturer in chief” to financial and human disaster.—News item, The Wave (Rockaway, New York).
Alpha Chi Omega President Megan Koelln issued a mea culpa apology.—LA Weekly.
In each example, the word apology is redundant. The only reason to follow mea culpa with the word apology would be in the context of talking about different kinds of apology.
Note: More often than not, the statement being described in the news as a mea culpa is not an apology at all, but an excuse.
excuse noun [eks-KYUS] : anything that justifies or extenuates a fault or defect.