Critical section = Is shared resource or part of program, not allowed to access by more than one process at same time.
Deadlock = Deadlock is a situation in which process waiting for resource, which hold by another process , which in turn waiting for resource hold by another process. in this way all process waiting for resource form cycle, and no process can complete its execution. this is called dead lock.
Mutual exclusion = Shared resource is not allowed to access by more than one process at same time is called mutual exclusion