VPIP/PFR/AF

VPIP is how frequently someone voluntarily puts money into the pot. Any hand some calls/raises preflop is counted, free flops seen from the big blind are not.

PFR is preflop raise. Same as VPIP except the player must raise/or reraise preflop to increase this stat.

AF is aggression factor. Someone with an AF of 1 bets and raises as often as they call. Someone with AF < 1 is calling more than betting (passive), someone with AF > 1 is betting/raising more than calling (aggressive).

Eg.

A player who is 30/15/3
He is playing 30% of his hands, raising 15% of his hands (i.e half the hands he plays he raises)
He is betting/raising 3x more frequently than he's calling so is pretty aggressive.