The buffer at the end of the Critical Chain. It determines the project completion date, and is the tool used by management and resources to make certain project decisions.
Size the Project Buffer based on the tasks in the feeding chain. The buffer size is the sum of a buffer for bias plus a buffer for variation. (Advanced Projects Institute)
Other Definitions
Project Buffer – The Project Buffer protects the promised due date from variation in the critical chain.(Frank Patrick’s Focused Performance Critical Chain FAQ)