Litecoin is a peer-to-peer cryptocurrency created by Charlie Lee. It was created based on the Bitcoin protocol but differs in terms of the hashing algorithm used. Litecoin uses the memory intensive Scrypt proof of work mining algorithm. Scrypt allows consumer-grade hardware such as GPU to mine those coins.
The transaction confirmation time taken for Litecoin is about 2.5 minutes on average (as compared to Bitcoin's 10 minutes). The Litecoin network is scheduled to cap at 84 million currency units.
Litecoin has inspired many other popular alternative currencies (eg. Dogecoin) because of its Scrypt hashing algorithm in order to prevent ASIC miners from mining those coins. However it is said that by the end of this year, Scrypt ASIC will enter the mass market.