H is O
H/O means 'highest offer,' like when you're trying to get a deal and you're just hoping someone will take it.
Your friend says, 'H/O is $20, so I'm taking it.'
You're at the store and the sign says 'H/O: $50, take it or leave it.'
Your mom says, 'H/O is $100, and I'm not letting you leave until you take it.'