There are three types of shotgun chokes:

Full choke

 The full choke is the tightest choke; it has the tightest shot pattern. This choke keeps the pellets together over a greater distance. Used it for longer shots, usually beyond 40 yards.

Modified choke

 The modified choke is not as tight as the full choke. Use it for mid-range shots, generally between 30 and 40 yards.

Improved cylinder choke

 The improved cylinder choke barely controls the spread of the shot. Use it for short-range shots, generally between 20 to 30 yards.