The two axes that define every player
Every poker type sits on two axes: how many hands they play (tight vs loose) and how aggressive they are when they do (passive vs aggressive). The four combinations give the four classic types. You measure this with VPIP (percentage of hands where they voluntarily put money in) and PFR (percentage where they raised preflop). VPIP 22 / PFR 18 is a textbook TAG; VPIP 45 / PFR 6 is a pure calling station.