What does com mean on a light switch?

Answer 1

In a situation where there is only one switch controlling the light or lights you normally use a spst (single pole single throw) switch that has only two connection terminals. This type of switch either connects or disconnects the two wires that are connected to the switch's terminals depending upon the position if the switch lever.

The com terminal on a light switch means that it is a three way or the kind of switch used where there are two or more switches that controll the same light or lights. The three way switch is a spdt ( single pole double throw) . If you look closely you will find this designation somewhere on the switch. On the spdt switch you have three terminals, a common and two branches. In one postiion the common connects to one branch and in the second position the common connects to the other branch.

If you are trying to install this switch in a situation where there is more than one switch controlling the light you must have the ability to correctly identify the common wire; if you can't do that you need help from someone who can do that correctly.