What type of switch is most commonly used for domestic purposes?

I assume that you are talking about electrical switches, when you say switches. There are a number of different electrical switches available in the market, depending on their function. 

The most commonly used switch, for domestic applications, is the one that controls one fixture and has a simple "on" and "off" feature. These are also known as single-pole switches. These simple switches are used to control the operation (on and off functions) of lighting fixtures,...

I assume that you are talking about electrical switches, when you say switches. There are a number of different electrical switches available in the market, depending on their function. 

The most commonly used switch, for domestic applications, is the one that controls one fixture and has a simple "on" and "off" feature. These are also known as single-pole switches. These simple switches are used to control the operation (on and off functions) of lighting fixtures, fans, etc. and are found throughout the house. In the "on" position, the electrical circuit is closed and the connected appliance functions. In the "off"position, the electrical circuit is open and the connected appliance does not operate. 

In comparison, other more complex switches (such as double-pole, multi-location, pressure switches, temperature switches, etc.) are used to control more than one device and may have other features. 

Hope this helps.