A "baseline" is a defined state through which "items" pass at a specific time during their life cycle. The establishment of a baseline is generally used to indicate that the associated items conform to some requirement or exhibit some characteristic.
A configuration baseline is a specific reference point of system definition to which changes or proposed changes may be related.
The completion of a project stage is determined by the satisfactory assessment of the quality of the defined products of that stage; these deliverables then form the "baseline" for the next project stage. Products of this next stage are then formally verified against the previous baseline as part of quality assessment before themselves becoming a new baseline. Each baseline must be documented and the quality assessment review recorded.