Satellite radio is a paid service not unlike cable television. It is a digital radio signal that is broadcast by a communications satellite which covers a much wider geographical range than a standard radio signal.
-A satellite tuner/receiver\012-A satellite antenna (most models come with the antenna)\012-A subscription to a satellite provider - either XM or SIRIUS. The two companies have merged but still exist has pseudo separate entities.
Some of the most popular features are:\012-Streaming weather, traffic and stock reports\012-A Tivo type program that allows you to record programs and listen to them later. \012-Favorite Song alerts - the program constantly scans for your pre-programmed favorite songs and/or artists.
My car is "satellite radio ready". What does that mean?
Typically, the car will have an in-dash radio that will work with a satellite radio tuner -- but the tuner itself, and the required antenna, are not yet installed.