'Gang' simply means the number of switches or sockets on a single faceplate. A 1-gang switch has one switch, a 2-gang switch has two switches side by side on the same plate, and so on.
Does Gang Refer to the Number of Circuits?
Not necessarily — a 2-gang switch plate has two separate switches, but each can control a completely different light or circuit. The gang number just describes the plate, not how the switches are wired.
How Do I Know How Many Gangs I Need?
This depends on how many separate switches or sockets you need at that location. If you're replacing an existing plate, matching the existing gang count is usually the simplest option — if you're planning new wiring, a qualified electrician can advise on the best layout.
Related guides
Shop designer light switches and plug sockets in 1, 2, 3 and 4 gang.