Plain meaning
Start with the shortest useful explanation before going deeper.
The multi-party pipeline through which maximal extractable value is captured: searchers identify profitable orderings, builders construct optimal blocks from bundles, relays facilitate trustless builder-proposer communication, and proposers select and finalize blocks. Over 90% of Ethereum L1 blocks flow through MEV-Boost. Proposer-builder separation (PBS) aims to formalize these roles at the protocol level.