This is copy/pasted from elsewhere, so don't think I like you guys enough to type all this shit out.
Anyway, the definitions will follow but don't get too much into the average ranges given. Those are for FULL RING at microlimits. Nutbags stats are 6-max and the ranges are significantly different.
VPIP: voluntarily put $ in pot (%). There is no sweet spot for this number, but the typical range is between 15 and 20. A few posters manage with sub-15 VPIP's and a few posters manage with VPIP's in the low 20's. As you move up, this number will often drop a point or two. Your VPIP will not be uniform across all positions. You should generally be tighter in EP than in LP.
PFR: preflop raise (%). The typical range is 7-10. A few posters exceed 10, but many posters begin their first 10K hands at or below 7. Some suggest that PFR should be half your VPIP, but that's an effectual coincidence and should not be your goal. If you only have a VPIP of 13 or 14, you will still often have the same PFR of 8-9 as someone with a higher VPIP. Your PFR will often be higher in LP than in EP.
VPIP from SB: typical range 25-35. This stat varies greatly by your table selection. If you typically play at passive games, you can expect this to be on the higher end. If you are in aggressive games, it will be lower. If its much lower than 25, you are missing out on a few profitable situations for the partial price. If its much higher than 35, you are probably playing too often and underestimating the difficulties of playing out of position postflop. Consult a starting hand chart for more information.
Saw flop all hands: This is an effect stat of your VPIP's and your table selection. It is often about 5% higher than your VPIP. Discussion at 2+2 primarily involves the VPIP stat rather than this one.
Steal defense: At the micro limits, this situation occurs very rarely and you will generally not have a significant sample size even after playing 20K hands. It is much better to focus on specific hands for defending situations as its often highly opponent dependent.
Attempt to steal: This situation occurs a bit more frequently than steal defense, but still it will not be too common until you hit the higher end of the micro limits. This number will often be in the mid-upper 30's, but will vary depending on your table selection and overall aggressiveness.
WSD: went to showdown. This number typical falls into the 28-32 range, but varies by your style. It is helpful in identifying potentially major leaks and too high a number often represents overly loose play on the big streets. Too low a number often represents a "fit or fold" mentality where you give up on too many profitable situations by ignoring the pot size.
WSF: won $ when saw flop. By coincidence, this number also falls into the 28-32 range. It is mostly an effect stat. If it is very high (35+) you may be running well. A number below 28 may indicate a problem with protecting your vulnerable hands or folding too many winners. Like many stats, a specific number does not indicate a specific problem, only that there may be one and you should be posting hands where you had difficult postflop decisions.
W$SD: won $ at showdown. Varies between 50-58. Below 50 often indicates that you are seeing too many showdowns while a number which is too high may indicate that you are folding too many winners. In limit Holdem, a pot is often quite large on the end, thus you often need to be quite sure that you don't have the best hand to make folding on the end correct.
FRB: folded to river bet. Varies between 40-55. This stat is pointless to analyze by itself. In combination with WSD or W$SD, it may indicate a problem of folding too much on the end (or not enough). As long as its not incredibly low or high, there are better ways to spend your time.
AF: aggression factor. This is an arbitrary number representing the relative frequency of which you are the aggressor on each street. The numbers vary greatly by your style and posting specific hands is generally better to determine if your aggressiveness is appropriate. VPIP/PFR account for your preflop aggression, so generally ignore AF - PF. Your postflop aggression will typically be around 2 - 3 on each postflop street. The flop is often higher than the turn and river, often exceeding 3.0. A micro posters overall AF (not including PF) will typically be in the 2.0 - 3.0 range. Some posters report success with overall AF's over 3, but nearly none have AF's under 2. This is not a stat worth overanalyzing unless it is woefully low or maniacally high.
when folds (%): This is not a stat worth overanalyzing as its speaks nothing of the appropriateness of your actions. Typical numbers may look something like this, but the range of "appropriate" numbers could be quite wide. (no fold: 12 _ PF: 75 _ flop: 8 _ turn: 3 _ river: 2).
check-raises: This is often in the 1% to 2% range of all possible actions. It is not worth analyzing this stat to decide if you are "check raising enough". Post hands to do that.
Win-rate: The number everyone is concerned about and the number we can do nothing about. Be happy with anything above 0 BB / 100 hands. The measure used is big bets per 100 hands. This accounts for multi-tabling and limit differences whereas $/hr gives you no real indication of success. Don't fret with something below 0 BB/100 if you have a small sample size. Variance and downswings happen and they can be quite large (200+ BB losses) and extend over a long period of time (10K+ hands). Your winrate will decrease as you move up in limits. Since its asked all the time, a 3 BB/100 winrate at .50/1.00 (online) is often regarded as great. 6 BB/100 is probably unsustainable. Once you reach 2/4 (online), 2 BB/100 is great for the long term and 4 BB/100 may be unsustainable. Also, you will be a loser from the blinds. The blind commitment is too great to overcome by solid play.
Now you know what they mean. The hard part is figuring out what the hell your stats mean to you.