WordNet (r) 3.0 (2006):

magnetic stripe
    n 1: a short strip of magnetic tape attached to a credit card or
         debit card; it contains data that will tell a reading
         device who you are and what your account number is, etc.

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

magnetic stripe

    A black stripe, printed on the back of a credit card
   or similar, that stores a machine-readable copy of the
   information on the card.  The stripe contains iron particles
   about 500 nanometers long that can be magnetised like
   magnetic tape.  The data can be read by swiping the card
   through a card reader.

   (2007-06-04)