The phrase "fist bump" refers to a friendly gesture where two people lightly hit their closed hands together as a way of saying hello or showing camaraderie. Full definition
He might be good for a nod or fist bump in the hallway, but he considers himself invisible to his peers at large. (dvdizzy.com)
I gave myself a mental fist bump and knew the only challenge now was getting in all the action we could before Mom was out of the doctors office, probably about 45 minutes. (soulemama.com)
If your child prefers fist bumps, waving, or blowing kisses, those are all great alternatives too. (happyyouhappyfamily.com)