The ampersand (&) is a logical language derived from the Latin word ET (meaning and). It is a logical language, which means that both of them belong to an indispensable relationship. It also means that one person and another person mean the same thing as and. For example, a & B means a and B, a and B, a × B.

The earliest history of the ampersand (&) can be traced back to the first century A.D., and is the earliest conjunction of the Latin ET (meaning and). The earliest & is the combination of E and t. after some evolution, it forms a fixed compound character, and then evolved into a symbol. This symbol is almost the same as the ET hyphenation of some ancient Western Fonts.

Source: @meredithmfields