Often talked about , exactly what does this mean ?

Hi Patrick

the baseline represents a snapshot of data at a particular time. This includes things like your task start, finish, duration, cost and work values. Once stored you can use the Tracking Gantt view to display your current and baseline positions - enabling you to quickly identify any slippage that might be taking place.

I hope this helps explain the purpose of the baseline. If you have any further questions please do let us know.

Kind regards,

Andrew

A baseline is effectively a snapshot of the project plan against which actual progress can be measured. It is often regarded as the "finalised plan", although strictly speaking as plans change during excecution no plan should be regarded as finalised until completed.
It is possible to save multiple baselines, so that for example the progress of the project can be measured from a number of different points in time. It is also possible to remove a baseline.