Plain meaning
Start with the shortest useful explanation before going deeper.
A collection of libraries, tools, and documentation for building applications on a specific platform. Solana SDKs include: @solana/web3.js (TypeScript client), solana-sdk/solana-program (Rust), Anchor (Rust framework + TS client), and Umi (Metaplex). SDKs abstract low-level details like serialization, signing, and RPC communication.