Mag is the short form of several words:

• Magazine, either as a periodical publication or a firearm component.
• Magnum, stemming from the latin word for large
• Magnet
• Magnification, in optical devices
• Magneto, an engine component (typically in the context of aviation)
• Magnesium alloy wheels, commonly called 'mags'
• Mines Advisory Group, a non-governmental organization (NGO) concerned with removal of debris of war (landmines, UXO etc)
• Magnesium float, a tool used in construction to smooth concrete
• The FN MAG machine gun