"1st ballot" means that a guy gets inducted the first time he's on the ballot.
For example, when Roger Clemens retires, I think he'll have to wait 5 years (or something like that) to be on the HOF ballot, and since he's one of the best pitchers ever, he'll be voted in the first time he's eligible. Hence, "1st ballot".
AHHHHHHHHH, gotcha