What is difference between critical path and longest path in P6?

In a schedule there can be more than one critical path but only one longest path which is also critical path. The longest path will define the overall duration of project.

I agreed with Mr.Y Zulfiqar Ali, and I'd like to briefly say that the Longest Path is a Critical Path, but not all Critical Paths are the Longest

CRITICAL PATH – is the longest continuous chain of activities (may be more than one path) which establishes the minimum overall project duration. A slippage or delay in completion of any activity by one time period will extend final completion correspondingly. The critical path by definition has no “float.”

LONGEST PATH (LP) – is the longest continuous path of activities through a project, which controls project early completion. It is possible for otherwise defined critical path activities to not be on the longest path and longest path activities to not show calculated critical float.

Critical Path is a path through your project which has activities YOU consider critical.

The Longest Path is the path through a project network from start to finish where the Total Duration is longer than any other path.

Critical Path activities are those activities whose total float = zero

Longest path is the shortest duration in which the project can be completed and all activities on the longest path will have zero total float ..................................................

I agree with Zulfiqar Ali theat Critical path establish minimum proejct duration and longest path controls proejct early completion