______means the act of a clearing corporation interposing itself between both parties of every trade, being the legal counterparty to both

The term you're referring to is "Central Counterparty Clearing" or "CCP". This is a process in financial markets where a clearing corporation acts as the counterparty to both sides of a transaction, reducing the risk of default by one party. Here are the steps:

1. Two parties agree to a trade.
2. The trade details are sent to the clearing corporation.
3. The clearing corporation, acting as the central counterparty, assumes the legal counterparty risk for the trade.
4. The clearing corporation matches and records all details of the trade.
5. The clearing corporation ensures that the trade is settled according to the agreed terms.
6. If one party defaults, the clearing corporation steps in to fulfill the obligations of the defaulting party.