A for Apple, B for Ball, C for Cat. It’s a useful way to teach children the sounds of the letters of the alphabet. Apple, ball and cat are just usefully short and common words that just happen to begin with the letter. They’re not the names of the letters, because in English we call the letters of the alphabet by invented words - ay, bee, see - that do no more than convey the sound that it represents (with the notable exception of the name for h, aitch, which doesn’t have an initial h in it).
But in some languages the names of the letters are words that have a meaning of their own. This is acrophony, the use of a word starting with a letter of the alphabet as the name of the letter.
From such pictographic symbols, Egyptian scribes derived the world's first alphabet by the principle of acrophony, in which a hieroglyph for a word came to represent the first consonant of that word. So, for example, the Egyptian word for “owl” began with an [m] sound, so the glyph for “owl” became the letter m.
An Introduction to Language and Linguistics, by Ralph W. Fasold and Jeff Connor-Linton, 2006.
The best-known cases are Classical Greek and Hebrew, both derived from ancient Phoenician. In Hebrew, for example, the first four letters of the alphabet are aleph (the Hebrew word for ox), beth (house), gimel (camel) and daleth (door). It’s as though our children’s alphabet had been transformed into the actual names for the letters, so that a wouldn’t be called or said ay, but apple.
There has long been a scholarly disputation about the source of the Phoenician and Hebrew alphabets, with some researchers arguing the names were merely a way by which scribes recalled the alphabet. However, it’s now agreed that these alphabets were originally hieroglyphs that pictured the objects named. As the hieroglyphs evolved into letters, the names were carried over with them.
Acrophony combines the Greek prefix acro– meaning uppermost or head, with –phony, sound, hence “the sound of the initial letter”.