Litecoin (LTC) is a peer-to-peer cryptocurrency and open source software project released under the MIT/X11 license. Inspired by and technically nearly identical to Bitcoin (BTC), Litecoin creation and transfer is based on an open source protocol and is not managed by any central authority. Litecoin is intended by its developers to improve upon Bitcoin, offering several key differences. As of November 2013, Litecoin had received extended coverage by mainstream media with agencies such as the Wall Street Journal, CNBC and The New York Times citing it as an alternative (or possibly even successor) to Bitcoin.
After Bitcoin and Ripple, Litecoin is the third-largest cryptocurrency by market capitalization.
A peer-to-peer network similar to Bitcoin's handles Litecoin's transactions, balances and issuance through scrypt, the proof-of-work scheme (Litecoins are issued when a small enough hash value is found, at which point a block is created, the process of finding these hashes and creating blocks is called mining). The issuing rate forms a geometric series, and the rate halves every 840,000 blocks, roughly every four years, reaching a final total of 84 million LTC.
If you want to know more then check out the full Litecoin Wikipedia article or watch the YouTube video below.