Card Readers
In short: Card readers read chip cards, magnetic stripe cards or memory cards.
In more detail: There are many kinds: memory card readers for SD cards, smartcard readers (signature card, ID card, health card) and payment terminals.
In Depth
Smartcard readers
Classes 1 to 3: class 1 has no keypad of its own, class 2 a PIN pad, class 3 additionally a display (more secure because the PIN does not go through the PC).
Memory card readers
For SD cards and microSD, connected to the computer by USB.
Payment cards
Terminals read chip, magnetic stripe or NFC (contactless) for Mastercard, Visa and others. See peripherals.
See also: Peripherals, SD Cards, NFC, Visa