A more thorough explanation:

A clearing agent is a person or company that acts as an intermediary in a securities transaction or provides facilities for comparing data with respect to securities transactions. This term includes a custodian of securities in connection with the central handling of securities. A clearing agent is responsible for ensuring that the transaction is settled properly and that the securities and funds are delivered to the appropriate parties.

For example, when you buy or sell stocks, a clearing agent ensures that the transaction is completed correctly. They make sure that the seller receives payment and the buyer receives the stocks they purchased. The clearing agent also ensures that the transaction is recorded accurately and that all necessary paperwork is completed.