Litecoin is a crypto currency. It is traded on some of the crypto currency exchanges. It has the symbol LTC.
Litecoin was one of the earlier altcoins and was introduced in 2011. It is very similar to Bitcoin except some tweaks such as decreased block generation time (2.5 minutes), increased maximum number of coins, different hashing algorithm (scrypt, instead of SHA-256).
It has remained one of the top altcoins possible due to it being introduced as one of the first altcoins. Also the different mining requirements made it popular among some miners because scrypt made it difficult to make FPGA and ASIC devices. The miners that could delay investing special FPGA and ASIC devices for a period of time. In the earlier days, it was possible to mine LTC using consumer hardware like CPUs and GPUs, but it is no longer profitable to do so since Scrypt based ASIC miners were released.