What means oh for three?

Answer 1

The "oh" is slang for zero. So the phrase would actually be zero for three if correct English were being used. This refers to zero successes for three tries at something. In Baseball this could mean the batter has had three attempts at hitting the ball but zero successes at making meaningful contact, that three players have been out to bat but zero have succeeded in making it back to home base, or the team has had three games but won none of them.