For the sake of clearly defining all of the different hardware devices that smart cards can be plugged into. Both terminals and readers read and write to smart cards. Readers come in many form factors and in a wide variety of capabilities. Another difference in reader types is the on board intelligence and capabilities or lack thereof. The options in terminal choice are just as wide.
Most units have their own operating systems and development tools.
They typically support other functions such as magstripe reading, modem functions and transaction printing.