That's Umbrella's drum tab isn't it. Fuiyoh... hip-hop beats.

Yeap, H is for the hi-hat (HH).
Don't know what "HP" stands for, but it seems to correspond with closing the HH with your foot. Honestly, I listened to the song to figure that out as even I've never seen "HP" before. Hat Plunge, perhaps =)

BTW, bass, not base.