Here are some simple definitions for the statistics you can find in weekly updates and player profiles.
GP – Games Played (登板): Any time a pitcher makes an appearance on the mound and throws a pitch, he adds to his games played total.
GS – Games Started (先発): When the pitcher is the first to appear on the mound for his team, he is credited as the starting pitcher.
W – Wins (勝利): The pitcher who is on the mound when the team scores the run that results in the team winning, and it is beyond the fifth inning, he gets credit for the win.
L – Losses (敗戦): The pitcher who allowed the opponent’s game-winning runner to get on base will be credited with a loss. Sometimes, he might allow the runner on base, get pulled for another pitcher, who allows that runner to score. Still, if he put the man on base, he gets the loss.
SV – Saves (セーブ): Various conditions apply to this statistic. A pitcher who (a) enters the game as a reliever and (b) faces enough hitters that the other team could tie the game, and (c) throws no more than three innings, and (d) closes the game successfully (i.e., his team wins), receives credit for a save. The most common form of save has the final reliever (the closer) coming in to pitch the ninth inning (hence, facing three batters) with a lead of three or fewer runs.
BS – Blown Saves: When a pitcher costs his team the lead in the seventh inning or later, he is charged with a blown save.
HLD – Holds (ホールド): When a relief pitcher comes in after the starter but before the closer and keeps his team in the lead, he is credited with a hold. It does not matter if he surrenders runs, as long as he does not give up the lead.
CG – Complete Games (完投): When a pitcher throws every pitch for his team in a game, he is credited with a complete game. Whether or not he wins or loses is irrelevant, he still records a CG.
SHO – Shutouts (完封): If the pitcher completes the game without surrendering a single run (earned or unearned), he gets credited with a shutout.
IP – Innings Pitched (投球回): The number of innings a pitcher completes. The number after the decimal indicates the number of outs he recorded in a partial inning. For example, 7.2 innings pitched means he completed seven innings and recorded two outs in the eighth.
H – Hits (被安打): The number of base hits the pitcher allowed to his opponents.
R – Runs (失点): The number of runs the opponents score as a result of runners who reached base during a pitcher’s time on the mound.
ER – Earned Runs (自責点): The number of runs the opponents score as a result of runners who reached base safely (not via an error or a wild pitch on strike three) during a pitcher’s time on the mound.
HR – Home Runs (被本塁打): The number of home runs the opponents score during a pitcher’s time on the mound. While inside the park home runs count here, a player who rounds the bases on their hit due to a fielding error will not be credited with a home run, hence it does not count as a home run against the pitcher, either.
BB – Walks (与四球): The number of times a player reaches first base after taking four balls (pitches outside the strike zone). This includes both intentional and unintentional walks, but not hit batsmen.
K – Strikeouts (奪三振): The number of times a pitcher gets three called strikes against a batter. This does not always result in an out, however. If the third pitch is not caught by the catcher, the batter has a chance to run to first base. If he reaches first before the throw, he is safe at first. However, the pitcher still receives credit for a strikeout. Also, if a hitter tries to bunt on third strike but hits a foul ball, it is ruled a strikeout.
ERA – Earned Run Average (防御率): The number of earned runs allowed divided by the number of innings pitched, multiplied by nine (the number of innings in a regulation ball game) gives you a pitcher’s ERA.
WHIP – Walks and Hits per Inning Pitched: The total number of walks plus the total number of hits (regardless of the number of bases earned) divided by the number of innings pitched gives you a pitcher’s WHIP.