Some sabermetric stat terms from Baseball Prospectus that you may see used here:
EqA - Equivalent Average. A measure of total offensive value per out, with corrections for league offensive level, home park, and team pitching. EQA considers batting as well as baserunning, but not the value of a position player's defense. The EqA adjusted for all-time also has a correction for league difficulty. The scale is deliberately set to approximate that of batting average. League average EqA is always equal to .260. EqA is derived from Raw EqA, which is (H + TB + 1.5*(BB + HBP + SB ) + SH + SF) divided by (AB + BB + HBP + SH + SF + CS + SB ). REqA is then normalized to account for league difficulty and scale to create EqA.
EqR - Equivalent Runs; EQR = 5 * OUT * EQA^2.5. In the fielding charts, the estimated number of EqR he had at the plate while playing this position in the field. In Adjusted Standings, EqR refers to the total number of equivalent runs scored by the team.
VORP - Value Over Replacement Player. The number of runs contributed beyond what a replacement-level player at the same position would contribute if given the same percentage of team plate appearances. VORP scores do not consider the quality of a player's defense.
WARP1 - Wins Above Replacement Player, level 1. The number of wins this player contributed, above what a replacement level hitter, fielder, and pitcher would have done, with adjustments only for within the season.
WARP2 - Wins Above Replacement Player, with difficulty added into the mix.
WARP3 - WARP-2, expanded to 162 games to compensate for shortened seasons. Initially, I was just going to use (162/season length) as the multiplier, but this seemed to overexpand the very short seasons of the 19th century. I settled on using (162/scheduled games) ** (2/3). So Ross Barnes' 7.4 wins in 1873, a 55 game season, only gets extended to 15.2 WARP, instead of a straight-line adjustment of 21.8.
RARP - Runs Above Replacement, Position-adjusted. A statistic that compares a hitter's Equivalent Run total to that of a replacement-level player who makes the same number of outs and plays the same position. A "replacement level" player is one who has .736 times as many EqR as the average for the position; that corresponds to a .351 winning percentage. Used when fielding data is unavailable.
FRAA - Fielding Runs Above Average.
FRAR - Fielding Runs Above Replacement. The difference between an average player and a replacement player is determined by the number of plays that position is called on to make. That makes the value at each position variable over time. In the all-time adjustments, an average catcher is set to 39 runs above replacement per 162 games, first base to 10, second to 29, third to 22, short to 33, center field to 24, left and right to 14.
Rate - A way to look at the fielder's rate of production, equal to 100 plus the number of runs above or below average this fielder is per 100 games. A player with a rate of 110 is 10 runs above average per 100 games, a player with an 87 is 13 runs below average per 100 games, etc.
Rate2 - See Rate. Rate2 incorporates adjustments for league difficulty and normalizes defensive statistics over time.
Pythagorean Record - A modified form of Bill James' pythagorean formula. Instead of using a fixed exponent (2, 1.83), the "pythagenport" formula derives the exponent from the run environment - the more runs per game, the higher the exponent. The formula for the exponent was X = .45 + 1.5 * log10 ((rs+ra)/g), and then winning percentage is calculated as (rs^x)/(rs^x + ra^x). The formula has been tested for run environments between 4 and 40 runs per game, but breaks down below 4 rpg. The original article is here.
After further review, I (Clay) have come to the conclusion that the so-called Smyth/Patriot method, aka Pythagenpat, is a better fit. In that, X=((rs+ra)/g)^.285, although there is some wiggle room for disagreement in the exponent. Anyway, that equation is simpler, more elegant, and gets the better answer over a wider range of runs scored than Pythagenport, including the mandatory value of 1 at 1 rpg. Go here for more.
NOTE: The league average for runs per game [RPG=(RS+RA)/G] is usually around 9, so one can usually quickly use 10 as the runs per win (RPW) in analyzing how the run metrics (VORP, RARP, FRAA, etc.) affect wins. However, if you wish for a clearer picture, the RPW formula is as follows: RPW = 2*(R-RA)*(R^x + RA^x)/(R^x - RA^x). Where R is the average runs scored per game and RA is the average runs allowed per game.
For the complete BP glossary, click this link: BP.com