The Collaborative International Dictionary of English v.0.48:

petting \petting\ n.
   Sexually titillating foreplay without contact with the
   genital organs.

   Syn: caressing, cuddling, fondling, hugging, kissing,
        necking, smooching, snuggling.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Pet \Pet\, v. t. [imp. & p. p. Petted; p. pr. & vb. n.
   Petting.]
   To treat as a pet; to fondle; to indulge; as, she was petted
   and spoiled.
   [1913 Webster]

WordNet (r) 3.0 (2006):

petting
    n 1: affectionate play (or foreplay without contact with the
         genital organs) [syn: caressing, cuddling, fondling,
         hugging, kissing, necking, petting, smooching,
         snuggling]