Cryptopedia
Multi-signature
It is a mechanism requiring multiple keys to authorize a transaction. Simply put, the assets stored on a multi-signature address can only be authorized when 2 or more signatures are provided at the same time. Such a mechanism further strengthens the asset security.
E.g.: Given that a multi-signature address is kept by A, B and C, you need at least 2 signatures among them if you want to authorize a transaction.