Plain meaning
Start with the shortest useful explanation before going deeper.
The JSON-RPC 2.0 protocol interface through which clients communicate with Solana nodes to query chain state, submit transactions, and subscribe to events. Solana exposes a rich set of HTTP and WebSocket endpoints (e.g., getAccountInfo, sendTransaction) that abstract direct peer-to-peer network participation, making RPC the primary integration point for wallets, dApps, and indexers.