A two way light switch can also be used as a one way light switch, that is a switch that turns a light (or lights) on and off from one switch, without any other switches being attached to that light circuit.
You would use a two way light switch when you have two switches controlling one light, for instance in a hallway, where you have a switch at both ends of the hallway that controls the hallway light. You are able to switch the light on and off from either end of the hallway.
You would use a one way light switch when it is the only switch controlling a light in a room, for instance if you have one door into your lounge, and you have a light switch next to the door.
If you have three switches that control the same light, for instance downstairs, in the hallways, upstairs, at the top of the stairs, and another one at the end of the landing, you would require the middle switch to be an intermediate light switch. You can read more about this on our 'What is an intermediate light switch' page.
As two way light switches are a lot more versatile that one way switches, and the price difference is negligible, we typically only sell two way light switches on our site (there are one or two exceptions in the Retrotouch range). This makes it a little easier to choose when ordering, and also caters for any changes that may happen during installation.