In a T20 match everyone follows one indicator or benchmark which is runs per over. For example, if run rate target set by team playing first inning is 8 per over then team playing 2nd inning should constantly score above 8 runs per over to finally win the match. So entire monitoring happens against runs per over as a benchmark or yardstick.
In a Project also we need such an indicator or yardstick so as to effectively chase it. In project such a yardstick is known as the Baseline.

There are total 3 baselines against scope, time and cost respectively.