The symbol & first appeared as one of the characters with the alphabet on the "hornbook sheet". It meant "and per se and"; now it is used as a short-hand for "and". The character itself is a conventionalized printed version of an abbreviatrion used for Latin et, "and".
The "hornbook" was a type of book made of a single page on which were printed capital (upper case) letters, small (lower case) letters, syllables, an exorcism, and part of the Lord's Prayer in a space less than three by four inches made for the teaching of reading. It was pasted on a paddle-shaped piece of wood and protected by a thin, transparent sheet of horn. Such a "book" was used as a primer in England and America from the 16th to the 18th centuries.