How does one define the term Critical Path? Is it the longest path? Is it the path with the lowest total float? Does the definition depend on the details of the project? After six decades of practicing the critical path method, is there a consensus definition for the concept at its core? This paper presents a proposal for revisions to AACE International Standard 10S-90 to clarify the definitions for Critical Path, Longest Path, and their related terms. Discussion and debate is encouraged prior to formal submittal of the proposed revisions to the Technical Board. Other technical societies that have sought to define these terms will be encouraged to reference or adopt AACE International’s definitions.