Master Securities Forward Transaction Agreement

Master Securities Forward Transaction Agreement, just one of the magnificent master agreements created by SIFMA, and intended to

... for use when parties enter into transactions for the purchase or sale of mortgage-backed and other asset-backed securities and such other securities as may be set forth, including pursuant to when-issued, TBA, dollar roll and other transactions that result or may result in the delayed delivery of securities...

... as if that is any more use to you as an explanation. Don't blame me: Blame SIFMA, which you can do by going here.