What is a Validator / Node Operator?
In blockchain ecosystems, the Node Operator runs what is called a node. A node can be thought of as a power pylon in the physical world, which helps to distribute electricity around a wide network of users.
Without these pylons, electricity would be largely centralised in one location; the pylons help to distribute power to entire wide-scale populations. And if one pylon fails, the grid is set up to circumvent this pylon and re-route the electricity to a different route.
Similarly, in blockchain infrastructure, each node runs an instance of the consensus protocol and helps to create a broad, robust network, with no single point of failure. A node failing will have little impact on the Network as a whole; however, if multiple nodes fail, or disagree with information entered into the transaction, then the block may not be signed, and there are fail-safe measures to notify the rest of the Node Operators of this.
The terms Validator and Node Operator are somewhat synonymous. Validator is the term used more commonly in the Cosmos documentation when referring to a Node Operator that is validating transactions on a blockchain. The only point worth mentioning is you can have a Node Operator that is NOT a Validator. These are known as Observer nodes, which play a more passive role on the network, as they don’t stake on the network or validate transactions, but can observe them.
The Cosmos Hub is based on Tendermint, which relies on a set of validators to secure the network. By ‘secure the network’, this refers to the way in which validators “participate in consensus by broadcasting votes which contain cryptographic signatures signed by their private key”. In English pls…
A cryptographic signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A private key is like a password — a string of letters and numbers — that allows you to access and manage your crypto funds (your mnemonic is a version of this). So, the above is saying validators can broadcast that they agree with transactions in a block, using their password to sign their agreement in a mathematical way which ensures security and privacy.