A baseline is a static copy of plan data that’s compared with actual and current data. It refers to a set of data about project that represents state before the work actually began.

Baselines helps to compare actual vs. planned. Baseline schedule means taking a copy of your schedule and set aside for comparison later on. A baseline is a snapshot/a picture of your project at a particular moment in time.

Baseline is a copy of the final approved schedule. It is the target to aim. As much is possible, the baseline should remain the same throughout the project.