Source : Webster's Revised Unabridged Dictionary (1913)

Playground \Play"ground`\, n.
   A piece of ground used for recreation; as, the playground of
   a school.

Source : WordNet®

playground
     n 1: an area where many people go for recreation [syn: {resort
          area}, {vacation spot}]
     2: yard consisting of an outdoor area for children's play

Source : Free On-Line Dictionary of Computing

Playground
     
        A visual language for children, developed for Apple's Vivarium
        Project.  OOPSLA 89 or 90?