Left on base can be viewed as both an individual statistic or as a team statistic.
In an individual batter's case, it refers to how many men remain on base after that batter makes an out at the plate, as the batter has failed to do his job to score those runners -- or at least put himself in a position to score.
In a team's case or in an individual pitcher's case, it refers to the number of men who remain on base at the end of an inning.
LOB can be a very circumstantial statistic on a game-by-game basis. But the best teams are usually good at finding a way to get runners home once they've reached base.
In A Call
"stranded," "runners stranded," "ducks left on the pond"