magnetic stripe

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A band of magnetic material in which tiny iron-based particles are used for data storage, used on swipecards.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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.