The gettxoutproof RPC command returns a hex-encoded proof showing that specific transaction IDs were included in a block. This proof is essentially a Merkle path which is useful for verifying that transactions are part of a block without requiring the entire block's data.

How is this used?

This command is used primarily for lightweight or SPV (Simplified Payment Verification) clients that do not download the entire blockchain but still require proof of transaction inclusion in a block. By obtaining a Merkle proof, these clients can verify transactions without needing the full block data, enabling more efficient storage and bandwidth usage while maintaining security assurances about transaction inclusion​