The Collaborative International Dictionary of English v.0.48:

fool around \fool` a*round"\, v. i. [imp. & p. p. Fooled
   around; p. pr. & vb. n. Fooling around.]
   1. To waste time in idle pursuits; to fool[2].

   Syn: fool[2].
        [PJC]

   2. To flirt or philander. --RHUDbr/ [PJC]

   3. To be sexually promiscuous; to engage in sexual
      intercourse with more than one partner; especially, to
      engage in adultery; as, to fool around with another woman.
      [PJC]