Magnetic Stripe Readers (a.k.a. MSR, Mag Stripe Reader, card swipe, swipe reader, stripe reader) are hardware devices that, when swiped, will read a credit, debit, gift, transit, security, or any other type of cardtype that has a magnetic stripe containing account information on the back.
MSRs are typically attached to the side of POS (point of sale) system monitors. Magnetic stripe readers can also be stand alone devices attached to a pin pad for manual number entry (like looking at a phone). Most readers sold today are three-stripe card readers, which will read the account number, name, and other information attached to that card. The interface in which the MSR connects will depend on the POS system and POS software.
Here are some examples of different types and placement of magnetic stripe readers: