What is uTorrent? How is it different from BitTorrent?

"µTorrent is just a different client for the Bittorrent protocol. µTorrent would have to be one of the most 'respected' and popular BitTorrent clients.

According to Wikipedia, BitTorrent is:

A peer-to-peer file sharing protocol used for distributing large amounts of data. BitTorrent is one of the most common protocols for transferring large files. BitTorrent protocol allows users to receive large amounts of data without putting the level of strain on their computers that would be needed for standard Internet hosting

Now this is where it starts getting a bit confusing. BitTorrent is:

A protocol
A software company
A program

The company BitTorrent, Inc. develops and distributes a program called BitTorrent which is just one of the many programs that work with the BitTorrent protocol. See this Lifehacker Hive Five on the Best BitTorrent Applications for other recommended BitTorrent clients

When people talk about 'torrents', they are most likely talking about the set of files they are downloading using the BitTorrent protocol."

"BitTorrent is a protocol for file sharing, uTorrent is a program that implements/uses this protocol to share files.

It's like the difference between HTTP and Firefox. Though Firefox is only a client (not a server); it only implements the client side of the protocol.

Though, there's also a program called BitTorrent, which was the original BitTorrent client, and according to wikipedia, it's now (after version 6.0) only a re-branded version of uTorrent."