In baseball, R.B.I. is an acronym for "runs batted in". This occurs when a person who is up to bat successfully hits the ball and causes a player who was on one of the bases to score a run. The batter receives however many R.B.I.'s that there were players who scored runs. The batter does not always need to land safe on a base to score an R.B.I., so long as he isn't the cause of the third and final out of the inning.
The batter hit a ball deep into the outfield while there were two people on base, one on second and one on third. Both scored so the batter got 2 R.B.I.'s, but the batter himself got thrown out at third, causing the second out of the inning.