Deadlock

 DEADLOCK n. A situation wherein two or more processes are unable to
       proceed because each is waiting for another to do something. A common
       example is a program communicating to a PTY or STY, which may find
       itself waiting for output from the PTY/STY before sending anything
       more to it, while the PTY/STY is similarly waiting for more input from
       the controlling program before outputting anything. (This particular
       flavor of deadlock is called "starvation". Another common
       flavor is "constipation", where each process is trying to
       send stuff to the other, but all buffers are full because nobody is
       reading anything.) See DEADLY EMBRACE.