gets it's name from modulator and demodulator which
are the functions that it does. For a modem to transmit data it
encodes the digital information to make it easier to transmit, and
then when it receives encoded information is demodulates it which
basically means it translates it.
send information a modem converts digital to analogue and then to
receive information again it converts analogue to digital.
In the case of a standard dialup modem that is why if you ever lift
up the telephone receiver
when you are connected to the internet you hear lots of strange
sounds. These sounds are the analogue signals going down the telephone
line both being received and transmitted.
are now mobile
broadband modems that are used to deliver broadband via mobile