Critical path is the process of looking at all the tasks within the project and calculating the optimal sequence to complete the project in the minimum amount of time. The critical path is NOT the sequence of mandatory tasks. Critical path analysis calculates the earliest and latest possible start and finish times for every project task to determine the amount of float available for each task in order to create a schedule of critical activities and dates based on the longest duration.
The critical path technique allows you to assess the impact of task delays. If tasks along the critical path are delayed, the timeline of the entire project will be impacted. If tasks outside of the critical path are delayed, they typically do not affect the timeline of the project unless the delay exceeds the float for that task. The critical path of the project can change throughout execution based on actual task start and end times, and duration or if tasks are changed.
Learn more about critical path analysis, or watch a video of an example.