The guaranteeing business gives a time-constrained guarantee to the asking business by staking its own trust rank. The given guarantee is fueled by tokens provided by the requesting party and issued on the Procurean network with a smart contract. All changes (positive or negative) to the trust rank of the requesting business are immediately reflected in the trust rank of the guaranteer for the remaining time, and the reward pool of tokens is redistributed to the guaranteer at the end of the guarantee period.

It's basically trust rank sharing for a certain period of time used by new businesses to enhance their trust rank.