WordNet (r) 3.0 (2006):

PID
    n 1: inflammation of the female pelvic organs (especially the
         Fallopian tubes) caused by infection by any of several
         microorganisms (chiefly gonococci and chlamydia); symptoms
         are abdominal pain and fever and foul-smelling vaginal
         discharge [syn: pelvic inflammatory disease, PID]

The Free On-line Dictionary of Computing (19 January 2023):

process identifier
PID
process ID

    (PID) An integer used by the Unix
   kernel to uniquely identify a process.  PIDs are returned by
   the fork system call and can be passed to wait() or
   kill() to perform actions on the given process.

   (1996-12-09)