Three dot combat sights are fixed, notch and post type sights that have, as the name indicates, three (white) dots. Two for the rear sight and one on the front sight. They are not illuminated like those manufactured by trijicon
Note that combat sights are commonly factory installed in fine firearms such as SIG
, and others.
The vital difference of a combat sight, as compared to say, a target sight, is how it is zeroed and aimed at a target. While target sights require you to align the sights then place your target or intended point of impact riding just above the front sight combat sights of the three dot type requires you to cover your intended point of impact with the front sight dot, of course while also keeping the rear and front sights aligned.
This is a small but vital difference that is good to know when shooting IDPA, IPSC, USPSA, or in actual combat. But always keep in mind that "a gun is only used to fight your way back to your rifle".