A modem stands for "modulator-demodulator". It is device which enables a connection of your home network, to the internet, provided through an internet service provider (ISP). A modem works by converting data from a digital format into modulated analog format for transmission in the form of analog signal to other telecommunication gadgets.
A modem enables digital data from a computer to be sent to the analog signal of a mobile phone. Modems perform dual function of modulating and demodulating data signals