The Graph is a decentralized protocol for indexing and querying blockchain data. The Graph makes it possible to query data that is difficult to query directly.
What is Graph Node?
Graph Node is the component which indexes subgraphs, and makes the resulting data available to query via a GraphQL API. As such it is central to the indexer stack, and correct operation of Graph Node is crucial to running a successful indexer.
What is Subgraph?
A subgraph extracts data from a blockchain, processing it and storing it so that it can be easily queried via GraphQL.