There are plenty of different terms used for the different sizes of 1911's. There are 5 basic styles that they can be grouped in. Long Slide - 6" slide on a full size frame. Government - 5" slide with a full size frame. The standard flush fit magazine typically holds 7 rounds. Commander - 4.25" slide with full size frame. There are some manufacturer's that use a 4" slide, but they are generally referred to as a "Commander." Concealed Carry Officer or CCO - 4.25" slide with Officer frame. Officer - 3.5" slide with Officer frame. The Officer is a shorter frame and the standard flush fit magazines hold 6 rounds. 3" slides are often referred to as an "Officer" as well.