A baseline is a logical name that can be attached to a certain state of a branch of your project. Normal, the state of your project is identified by the timestamp of the run that computed the project state. A baseline is a convenient way to refer to such a state (instead of a date).
A baseline can be used to compare the last run to (otherwise, the last run is compared to the run 30 days ago). A baseline can be used to mark a milestone in your development process.
To set a baseline, see TICSMaintenance -setbaseline.
It is also possible to automatically set a baseline after branch calculation: TICSQServer -setbaseline.