A magnetic stripe is a thin strip of magnetic material found on the back of cards like credit cards, debit cards, and identification cards. It contains encoded data that can be read by a card reader. This data typically includes information such as the cardholder's name, account number, and expiration date. When a card with a magnetic stripe is swiped through a reader, the magnetic field is disrupted, allowing the reader to decode the information stored on the stripe. This technology is widely used in various industries for secure transactions and access control, making it an essential part of modern payment systems and identification methods.