I'm not sure if I would say that it is necessarily "backed" by money but it is most certainly relative to money. If it were backed, then it's value would be determined by one unit of something (say, the dollar), and it would be subject to being used in the event that the bitcoin wouldn't be there. The US dollar was backed by gold until several decades ago, but then they removed that in order to have better control over it. So now the Federal reserve can print as much as it wants to determine how much value it holds in the country.

Bitcoin is exchangeable for other money but is more independent.