If you're talking about fig. 4, then it's some units scaled so that random performance is 0 and perfect performance is 100 (depending on task it may be accuracy

If you're talking about fig. 4, then it's some units scaled so that random performance is 0 and perfect performance is 100 (depending on task it may be accuracy or something else). Since the models are so large, good benchmarks are diverse, and different tasks require different metrics.