The Collaborative International Dictionary of English v.0.48:

Sandman \Sand"man`\, n.
   A mythical person who makes children sleepy, so that they rub
   their eyes as if there were sand in them.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sandman
    n 1: an elf in fairy stories who sprinkles sand in children's
         eyes to make them sleepy

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

Sandman

   The DoD requirements that led to APSE.