What is a deadlock?

Dead Locks is a term specially used in "Operating Systems" for such a situation in which two or more processes fetching for resources in such a way that no process will gain the resource because particular resource is already engaged with second process. :-)

relevant wiki links:

http://en.wikipedia.org/wiki/Deadlock

http://en.wikipedia.org/wiki/Dining_philosophers_problem

A deadlock occurs when two or more processes are waiting on the same resource and each process is waiting on the other process to complete before moving forward.