Chris asked for an explanation on a couple of stats in the comments for the last post, and I started responding there, but the post got really long and I figured I’d throw it in the main feed here instead.
Anyway, Fangraphs.com and baseball-reference.com have pretty extensive glossaries, so I urge you to read (way, way) more about the subject there.
I normally use stats to inform my writing more than drive them, but the stats Chris asked for all might very well come up here, so here goes:
Briefly: WAR stands for Wins Above Replacement, and uses both offense and defensive stats in an attempt to determine precisely how many wins a player is worth to his team above the replacement-level player at his position (think Alex Cora).
WAR relies on UZR, or Ultimate Zone Rating, to measure a player’s defense. UZR is a pretty complicated metric, but it essentially tracks how many outs a player converts on balls hit within his “zone of responsibility.” A 7.6 UZR would mean a player saved his team 7.6 runs defensively over the replacement defender at his position over the course of a season.
OPS+ and ERA+ are just versions of OPS and ERA that are scaled a bit differently. Essentially, they’re park- and league-adjusted to better compair players of different eras and ballparks, and they’re weighted so the average is 100 and higher numbers are better. So a player with a 160 OPS+ hit 60 percent better than the average hitter would in his same situation.
The good general point of reference those two stats — and they’re two of my favorites, since they’re quick and easy but still fair for comparisons — are SAT scores, since they’re weighted the same way and the range is usually about the same. The worst players in the league will score around 60 and the best around 160, though there are always a few outliers.
BABIP refers to batting average on balls in play. It is mostly used to measure luck, because a player’s BABIP usually remains around the same level across his career, and years in which it is abnormally high or low might signify good or bad luck. It’s a bit more complex than that, of course, because BABIP corresponds pretty closely to line-drive rate and a player might be getting more hits on balls in play because he’s actually hitting the ball harder.
Tedquarters 
Great stuff, thanks. Something else I always wonder about since we are on the subject of odd stats, is something that is commonly brought up on MLB broadcasts, mainly FOX, withing many of thier dumb graphics.
What always gets me are stats like a hitters batting average on “balls low and away”, or batting average “on balls inside” (yes I am looking at you FOX hot/cold chart). How exactly do they calculate a players batting average on olny pitches in a particular location?