Bitcoin TOP (BTT) is a fork of Bitcoin that occurs at the predetermined height of block 501118 and therewith a new chain will be generated as the BTT. Bitcoin TOP miners will begin creating blocks with a new proof-of-work algorithm, and will consecutively develop and enhance the protection for account transfer and privacy based on original features of BTC. This will cause a bifurcation of the Bitcoin blockchain. The original Bitcoin blockchain will continue unaltered, but a new branch of the blockchain will split off from the original chain. It shares the same transaction history with Bitcoin until it starts branching and coming into a unique block from which it diverges. As a result of this process, a new cryptocurrency was created which we call “Bitcoin TOP”.
http://www.bitcointop.org/faq.html