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

Single Edge Contact Cartridge
SEC
SECC

    (SEC, SECC) The cased daughterboard housing
   Intel's Pentium II, Pentium III, and Xeon
   microprocessors.

   A SECC fits into a Slot 1 or Slot 2 connector.

   [SECC 2?]

   (1999-08-05)