Fixed sights are "non-adjustable," though on most autos, the rear sight can be drifted in the dovetail to change the windage (the lateral point of impact). So if the pistol is shooting to the right or left, you can often correct it by moving the rear sight, but you may need to change something if the gun shoots high or low. I prefer fixed sights on defense guns, but adjustables are good for guns that live an easier life.
Night sights glow in the dark, and typically consist of small vials of radioactive tritium embedded in the sights. Trijicon is a manufacturer of tritium night sights (among other things). There are several other good such manufacturers, including Meprolight, which is my preference in night sights.
I've not heard of "contrast sights."