Phaser Type III
From StarFleet Bureau of Information
The type III phaser, the phaser rifle, is carried in most ship stores for emergency situations. Type I and type II weapons are suitable for most situations. The type III has the same 16 beam settings of the type II, a multiple target acquisition system, a gyrostabilized beam emitter, and a larger power reserve than either the type I or II.
The type IIIa is a compact "phaser carbine" which has the capabilities of a standard phaser rifle in a smaller overall form factor. Its stabilization system is generally considered to be less effective than the standard type III.
The Type IIIc is a compact "bullpup"-style phaser rifle meant for close-quarters fighting. It has a heavier stock which can, itself, be used as a melee weapon.