Final answer:
In a PERT chart, the critical path is defined by several items, and the estimated and actual activity budget is typically not one of them.
Step-by-step explanation:
In a PERT chart, the critical path represents the sequence of activities that must be completed in order to complete the project on time. Each milestone on the critical path is defined by several items. The options provided in the question are: planned start and finish dates, specific task milestone name, actual start and finish dates, and estimated and actual activity budget. Typically, the item that is not part of the definition of each milestone on the critical path is estimated and actual activity budget. This item is related to the cost management of the project, while the critical path focuses on the schedule.