'Critical path' can be defined as the longest estimated sequence of interdependent activities (WBS items) that must be completed on time to ensure that the project is completed on the due-date. The critical path activities are performed under the 'predecessor-successor' relationship, which means that any next activity cannot be started until its predecessor has been completed.

Each WBS item on the critical path is a critical WBS item. There can be more than one critical path in a project.