The Collaborative International Dictionary of English v.0.48:

mag tape \mag tape\ n.
   Same as magnetic tape.

   Syn: magnetic tape, tape.
        [PJC]

WordNet (r) 3.0 (2006):

mag tape
    n 1: memory device consisting of a long thin plastic strip
         coated with iron oxide; used to record audio or video
         signals or to store computer information; "he took along a
         dozen tapes to record the interview" [syn: magnetic tape,
         mag tape, tape]