&: The History of

The ampersand is a ligature (combination) of the cursive
letters "e" and "t", invented in 63 BC by Marcus Tirus [Tiro?]
as shorthand for the Latin word for "and", "et".

The word ampersand is a conflation (combination) of "and, per
se and". Per se means "by itself", and so the phrase
translates to "&, standing by itself, means 'and'". This was
at the end of the alphabet as it was recited by children in
old English schools. The words ran together and were
associated with "&". The "ampersand" spelling dates from
1837.

Thanks Dictionary.com!

An ampersand (&, &, &), also commonly called an and sign, is a logogram representing the conjunction "and."
...The ampersand often appeared as a letter at the end of the Latin alphabet, as for example in Byrhtferð's list of letters from 1011.[1] It is thought that teaching & as the last letter of the alphabet (... X Y Z and &), a common practice through the 19th century, led to its name, a corruption of the phrase "and per se and", meaning "and [the symbol which] by itself [is] and". The Scots and Scottish English name for & is epershand, derived from "et per se and" with the same meaning.
More of the history of & at Wikipedia