Packet Radio (PR in the following) is a data transmission mode used in Amateur Radio, which is based on protocols similar to those on the internet, in particular AX.25, which is a subform of the X.25 protocol, just with limited length of data blocks, the so-called packets.
PR networks allow regional, national and even intercontinental delivery of e-mail and other data transfer, but restricted to radio amateurs. TCP/IP is also in use on packet radio, allowing the use of all the high-level protocols like HTTPorFTP known from the internet.
Each PR station consists of at least one transceiver with antenna and one TNC (Terminal Node Controller). Normal PR stations also have a terminal (which may be emulated by a computer), to allow operator interaction with the TNC, but automatic PR stations do not need a terminal.