Cosmos is a decentralized protocol for facilitating secure communication and transactability between existing blockchains without the need for a centralized intermediary. In addition to this, Cosmos provides the infrastructure to build new, scalable blockchains within a connected ecosystem.

Traditionally, independent blockchains cannot communicate with each other securely. For example, a payment on the Bitcoin blockchain can't be triggered by code in an Ethereum smart contract - that is unless they are connected to each other via Cosmos.

Cosmos has a native proof-of-stake token called ATOM that incentivizes people to validate transactions.

Proof-of-stake just means that transactions on the Cosmos network are validated by people who stake their ATOM in order to receive block rewards and transaction fees. This keeps the network secure because stakers who act maliciously will lose their ATOM tokens.