Golf Club Irons are specifically the golf clubs with heads made of usually carbon steel. These normally come in a set numbered from 3 to 9 with Pitching Wedge or 10 and Sand Wedge but can have 1 or 2 for the specialist. All Golf Club Wedges are also strictly speaking iron clubs but they are usually bought separately as you develop your game.
Each iron has a shaft of differing length with 1 being the longest, hence low numbers are referred to as long-irons, then mid-irons while the high numbers are short irons. The shafts also come in either metal shaft or carbon graphite shafts. All shafts can be varied for length and stiffness if you are getting them custom fitted. When custom fitting irons you get to choose the make of shafts and also of grips that will be fitted.