PFR (Pr Flop Raise) shows the percentage of how often a player raises before the flop. PFR is a more specific version of VPIP. This stat is useful when comparing it with VPIP stat. PFR is usually lower or close to VPIP.

If a large part of a player’s VPIP is made up by his PFR (e. g. 25/22), he’s an aggressive player.

If PFR makes only a small part of VPIP (e. g. 25 / 5), a player is passive.

So VPIP alone tells if a player is tight or loose. And a combination of VPIP/PFR tell if he’s aggressive or passive.

You should ideally be raising at least 70% of the time you enter a pot (e. g. 20%/>=14%). If your VPIP/PFR ratio is less than that, you should be more aggressive and raise more instead of calling preflop.

VPIP/PFR shows a player’s playing style.

More @ http://www.thepokerbank.com/articles/software/pfr/

VPIP (Voluntarily Putting money In to the Pot) shows how often a player is getting involved in pots (calling or raising) before the flop. E. g.  if you played 100 hands and called/raised 25 hands, your VPIP will be 25%. Note: The small blind and big blind do not count toward your VPIP, as you did not voluntarily put this money in to the pot.

VPIP < 24% –  indicates a tighter play. The player will not be raising to steal blinds, will not be calling with lower connectors. He only plays when he has something.

VPIP > 30 % – indicates a looser play. The player will be raising to steal blinds, will be calling with connectors, etc.

It’s hard to win long term with a high VPIP.

More @ http://www.thepokerbank.com/articles/software/vpip/