Pay-to-Witness-Script-Hash (P2WSH) is an address format and type of transaction that allows funds to be sent to a script hash (a cryptographic hash of a script) instead of a public key hash. This allows for more complex transactions than the traditional Pay-to-Public-Key-Hash (P2PKH) address format, as well as the ability to use SegWit script types in a backward compatible manner.
P2WSH is a feature of the Bitcoin protocol introduced in 2017. It is an improvement over the previous address format, Pay-to-Public-Key-Hash (P2PKH), which requires a single public key hash to be specified. With P2WSH, a script hash is used instead, allowing for more complex transactions. P2WSH transactions are more efficient than their P2PKH counterparts. Since the transaction is sending to a script, rather than a public key, the amount of data required to be included in the transaction is reduced. This reduces the size of the transaction and allows it to be propagated more quickly across the network.
P2WSH also allows for the use of SegWit script types in a backward compatible manner. This is possible because the script hash is provided in the transaction, allowing the transaction to be validated without needing to know the entire script. This allows for the use of SegWit script types without having to upgrade all nodes in the network to support them.
Overall, P2WSH is an important addition to the Bitcoin protocol, as it provides an efficient and backward compatible way to use more complex script types. This allows for more powerful and secure transactions, as well as the ability to use SegWit script types with older nodes.