The Free On-line Dictionary of Computing (30 December 2018):

Slot 2

    A physical and electrical specification
   for the 330-lead edge-connector used by some of Intel's
   microprocessor cards, currently (August 1999) the SECC
   Pentium III/Xeon.

   Slot 2 is intended for use in high end multi-processor
   workstations and servers.

   See also Slot A, Slot 1.

   [Multi processor support?]

   (1999-08-04)