VP$IP

VP$IP (or voluntarily put money in the pot) is a measure of a player's loose or tight play used by Poker Tracker and other analytical tools. This is often abbreviated as "VPIP" by the lazy.

VP$IP is expressed as a percentage of the time a player puts money into a pot to see a flop in Hold'em. The big blind is not considered voluntary, so if a player checks his big blind, that is not considered in the VP$IP calculation. However, if the big blind calls a raise, then it is considered for VP$IP. If a player calls or raises only to fold to a further pre-flop raise, this also counts for VP$IP

Someone with a VP$IP of about 20% or less is considered a tight player. If the percentage raises above 25% or so the player is probably playing too loose to be correct. This assumes a full ring game, however. Players who only play short handed games or small sit-n-go tournaments will have a higher VP$IP.