GU10 bulbs have a 2 pin connector with 'feet' at the bottom of each pin, the center of the pins are 10mm apart. The feet are used to lock the bulb into place when it is twisted in the lamp holder. Because of this they are sometimes called 'twist and lock' bulbs. GU10 bulbs all run at mains voltage.
There are many options available, with current models being either halogen or LED GU10 bulbs. Before LED GU10s became popular it was common to use fluorescent spot bulbs.
GU10 spot bulbs are most often used in recessed downlights and surface mounted spot fittings.