There are two possible answers to this. If the H is listed next to the ER (earned runs), SO (strike outs) and BB (base on balls), it is a number of hits that the pitcher gave up. However, if you see it right after the pitcher's name: Joe Bozo (H, 1), then it stands for a "Hold" and the number right after that is the number of Holds he has been credited:
A Hold is credited any time a relief pitcher enters a game in a Save Situation, records at least one out, and leaves the game never having relinquished the lead. Note: a pitcher cannot finish the game and receive credit for a Hold, nor can he earn a hold and a save.
On Base Percentage
Intentional Base on Balls
It stands for a "blown save"
A batter's box is one of two areas in baseball beside home plate in which a batter is required to stand during an at-bat.
Walks plus hits per innings pitched.
k stands for strikeout looking K stands for strikeout swinging