Kanji come from "temp" and "face" so would literally mean "temporary face".
It's the first part of the name of the Kamen Rider series which is often translated as Masked Rider.
A main character on Bishoujo Senshi Sailor Moon is called Tuxedo Kamen, which is often translated to Tuxedo Mask.
Men - The second half of Kamen can also mean "mask" when by itself. It also means "surface" or "face", so the meaning is dependent on the context in which it's used.
Fukumen - Another word for "mask".