A common symbol for "and", used as the "address of" operator in C, the "reference" operator in C++ and a bitwise and or logical and operator in several programming languages. Visual BASIC uses it as the string concatenation operator and to prefix octal and hexadecimal numbers.
UNIX shells use the character to indicate that a task should be run in the background (single "&" suffix) or (following C's lazy and), in a compound command of the form "a && b" to indicate that the command b should only be run if command a terminates successfully.
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.