SPV means a simplified payment verification. In short, SPV allows you to validate your transactions without worrying about anyone’s transactions. This ensures that your transactions are in one block. The SPV client does not need to run a full node (that is, download the entire chain). They can simply create a bloom filter of the transactions that interest them and download those transactions based on the filter. They can validate that the Merkle tree contains a transaction output that pays for them and that it comes from a block with valid proof of work. Due to the structure of the Merkle tree, it can be pruned to contain only relevant transactions for the client without modifying the hash included in the block header, which saves a lot of time, effort and space over sending everything.