Thrusting is when you're up against someone kinda humping them but just pushing them closer to you or yourself onto them at the main waist point. Girls especially love it when being kissed and then pulled up against whoever by having that person's hands on their butt and being pulled. Guys seem to like it the opposite, when the girl is the one pulling on the guy. Since some guys don't like their ass being touched, girls will usually grab the side of the guy's pants.
Boy #1: Oh my god, last night i was kissing my gf and she totally started thrusting me.
Boy #2: That's normal, i do that to my gf and she loves it.