bip 37

BIP 37 (Bitcoin Improvement Proposal 37) specifies the use of **Bloom filters** in the Bitcoin network to enable **lightweight (SPV) clients** to efficiently receive relevant transactions without downloading the entire blockchain. It allows a client to ask full nodes for transactions that match a filter, improving privacy and bandwidth usage, though it later became known for privacy weaknesses and has been deprecated in favor of newer approaches like BIP 157/158.