The term baseline start date applies to the actual scheduled start date of a schedule activity within the approved schedule baseline. The baseline start date will typically be estimated at the onset of a schedule activity based on a determination of how much work needs to be done, how many team members will be required to complete it, which specific team members should be involved in the process (and concurrently what their schedules may look like in regards to availability), and what resources may be needed. The baseline start date may be adjusted prior to n activity’s kickoff if it has become apparent that delays in preceding activities will make the previously determined baseline start date impossible to meet. Provided the project team is able to secure the necessary approvals to do so, the baseline start date can be modified based on the requirements necessary. See also scheduled start date.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.