Mac can be:

• A nickname for the Apple Macintosh computer
• A nickname for McMaster University, Canada
• A nickname for Jim "Mattress Mac" McIngvale, from Houston
• An abbreviation for macaroni
• The mac, formerly Midlands Arts Centre, a venue in Birmingham, England.
• Mac Gimse
• An Irish and Scottish Gaelic word indicating "son (of)", resulting in surnames derived from family lineages e.g. "MacChionnich" -- "son of Coinneach", translated into English as Mc as in McCarthy. These names are not, however, patronymic but derive from historical or legendary forefathers.
• A short form for the famous Big Mac hamburger, sold at McDonald's.

It is also a Three letter acronym, see MAC.