WHIP:
Walks + Hits per Inning Pitched. Measures baserunners allowed. Lower is better.
K/9:
Strikeouts per 9 innings. Measures dominance and swing-and-miss stuff.
K/BB Ratio:
Strikeouts to walks ratio. Shows control and command. Above 3.0 is good.
Quality Start:
6+ innings pitched with 3 or fewer earned runs. Measures consistency.