See previous nodes (press Search after it loads) on the subject as well. In Unix they are called zombie processes.
What you are seeing is that a data structure containing exit information from the process that died is waiting to be read by the parent process. The spot that the OS stores this information is in the process table (well, close enough for this discussion). You need to use wait or waitpid to capture the information. These functions tell the OS that it can now release the information and clear that slot in the process table.