Among elementary school children and their parents and teachers, another name for the alphabet. As in, "Now I know my ABC's, next time won't you sing with me?"

Of course, the word alphabet comes from alpha and beta, the first two letters of the Greek alphabet. So perhaps the major civilization that's around a couple thousand years from now will have a similar alphabet, but refer to it as their Aybeecee (with the emphasis on the first syllable).