Plain meaning
Start with the shortest useful explanation before going deeper.
The Solana RPC method that submits a fully signed, serialized transaction to the cluster for processing. The transaction is passed as a base64-encoded string. By default, the RPC node performs preflight checks (simulation) before forwarding to the leader; this can be disabled with skipPreflight for lower latency at the risk of submitting invalid transactions. The method returns the transaction signature immediately without waiting for confirmation. Clients must separately poll or subscribe for confirmation status.