Pistols are a important part of airsofting, most fields require that when within 20 feet of someone, you must switch to a sidearm as to not injure them with rifles. They are also very effective when you run out of ammo
Gas blow backs
Gas blow back pistols are the most common type of sidearm available. They are the most realistic pistols available. The term Gas Blow Back (GBB) refers to the action the gun performs when the trigger is pulled. After the BB is loaded by racking back the slide, the hammer is in the firing position. When the trigger is pulled the hammer is released and an internal hammer presses a valve release on the back of the magazine. When the gas is released, the BB is expelled out of the barrel and the slide (the moving part on the top of the gun) cycles and the hammer is reset and the next BB is loaded. There are all kinds of different gas pistols: Gas Blow Backs that use propane, greengas and redgas; CO2 Gas Blow Backs that use a 12g CO2 cartridge (tend to be the more powerful pistols); and Japanes guns (Tokyo Marui) that use a special gas called 134a gas that is made for plastic Blow Back guns.
Non blow back
Similar to gas blow back's in effectiveness and performance, they are slightly cheaper for the most part. Most operate only on CO2 with the chamber for the CO2 cartrage built into the gun itself instead of being housed in the magazine like in most gas pistols. Most have a longer trigger pull because nothing recocks the hammer after each shot.
Automatic electric pistols
Less common than gas guns, they can be somewhat effective but have much less power than gas guns but are overall cheaper to maintain and use. It is an electric powered airsoft handgun with a gearbox that can usually be upgraded and uses a rechargeable battery. They range anywhere from 150-250 fps.