Usage: LUSERS [<wildcard> [<server>]]
  Gives a brief listing of the number of visible users, the
  number of invisible users (marked UMODE +i), servers and
  the number of operators.

  Given a wildcard mask such as
    LUSERS *.edu
  it will count up the number of servers and users that match.
  If you add a <server>, it'll be asked for the above information.