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 HTTP or FTP 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.