Avalanche is a blockchain platform launched in 2020, built around a goal of combining high transaction speed with strong decentralization, two properties that are often difficult to achieve together. It uses a novel consensus protocol that allows it to confirm transactions in a matter of seconds.
A distinguishing feature of Avalanche is its multi-chain structure, which separates the network into different chains for different purposes, including one specifically designed for creating custom blockchains, similar in spirit to Polkadot's parachain concept but built with a different underlying technical approach.
The native token, AVAX, is used to pay transaction fees, participate in staking to help secure the network, and serves as the base currency across the broader Avalanche ecosystem of applications.