The alphabet

The English word alphabet came into Middle English from the Late Latin word alphabetum, which in turn originated in the Greekἀλφάβητος (alphabētos). The Greek word was made from the first two letters, alpha and beta.[7] The names for the Greek letters came from the first two letters of the Phoenician alphabet; aleph, which also meant ox, and bet, which also meant house.

Sometimes, like in the alphabet song in English, the term "ABCs" is used instead of the word "alphabet" (Now I know my ABCs...). "Knowing one's ABCs", in general, can be used as a metaphor for knowing the basics about anything.