An alias is normally an alternative name someone may use for themselves, often to prevent their true identity from being known. They are often used by criminals as well as for espionage purposes. It can also be an adverb as well as a noun and mean, 'otherwise known as'. In this case it might be used as, "John Smith alias Richard Jones was identified as the suspect". The plural of alias is aliases.
In computing, an alias is an alternative name for a file, address, command, or other item, and can be used to access or find it.
The word 'alias' derives from the Latin, alius. The first known use of 'alias' as a noun dates back to 1605 and as an adverb to some point between 1525-1535.