Plain meaning
Start with the shortest useful explanation before going deeper.
The data serialization format used to represent account data in Solana RPC responses. Supported encodings include base58 (human-readable but slow for large data), base64 (efficient binary encoding, most common), base64+zstd (compressed base64 for large accounts), and jsonParsed (structured JSON for known programs like SPL Token and System Program). The encoding parameter is specified per-request and affects response size and parse complexity on the client side.