LIGO is a programming language that aims to provide developers with an uncomplicated and safer way to implement smart-contracts. LIGO is currently being implemented for the Tezos blockchain and as a result, it compiles down to Michelson - the native smart-contract language of Tezos.
Smart-contracts are programs that run within a blockchain network.
LIGO was initially meant to be a language for developing Marigold, on top of a hacky framework called Meta-Michelson. However, due to the attention received by the Tezos community, a decision has been put into action to develop LIGO as a standalone language that will support Tezos directly as well.