It is satellite radio. I believe it is only available in the US.
It costs about $9 per month, but given the current state of on-air radio, for me it is well worth the cost. Lots of good music (including a lot of U2), lots of sports.
I'm sure SIRIUS satellite radio is good too. The only major difference between the two services I'm aware of are their sports packages and a slight difference in subscription price.