1. A secondary or symbolic name for a file, a collection of data, or a computer device. In a spreadsheet, a range name, such as Income, is an alias for a range, such as A3..K3. In networks, group aliases provide a handy way to send electronic mailed two or more people simultaneously. From QUECID

2. An alternate name, or abbreviation, used in place of a command or a sequence of commands in the C shell and the Korn shell. From Linux Guide @FirstLinux

3. The word alias is used for many different things within infosec. In all its definitions, it generally means somesort of alternate name for something. Some definitions used for alias are: e-mail alias