Suretyship
An aval is a bill of exchange undertaking, by which a person (the avalist), having issued it, assumes responsibility for the performance of obligations by any of the persons liable under the bill of exchange - the acceptor, drawer, or indorser; it is executed either by the avalist's guarantee endorsement on the bill of exchange or an additional sheet (allonge), or by issuing a separate document. The scope and nature of the avalist's liability corresponds to the scope and nature of the liability of the person for whom the aval was given. An avalist who has paid the bill of exchange is entitled to claim reimbursement from the person for whom he gave the aval, as well as from persons liable to the latter. An aval increases the reliability of the bill of exchange and thus promotes its circulation.
Source: Letter of the Central Bank of Russia dated 09.09.1991 No. 14-3/30 "On banking operations with bills of exchange"