One meaning for the word zombie:
An insecure computer that’s compromised by a worm or Trojan horse and used in either distributed denial of service (DDoS) attacks or spamming sessions. Compromised computers usually have a bot installed that listens for commands and then executes DDoS or spamming whatnot with no input from the legitimate owner/user.
A zombie can also refer to a child process that has finished its task but hasn’t been terminated by its parent process.