> What is a "handle" exactly? What kind of system call creates it?

In a Win32 context, a handle is any kernel handle which includes but is
not limited to: files, sockets, shared memory, synchronization objects,
etc. For the original reporter, a tool such as
http://www.sysinternals.com/ntw2k/freeware/procexp.shtml will help in
identifying exactly what kind of handle is not being closed.

Greg Hewgill
http://hewgill.com