Ryoji refers to a document issued under the Ritsuryo system (a system of centralized government based on the ritsuryo code by princes, empresses, etc.) for conveying orders of princes and three sango (Grand Empress Dowager, Empress Dowager, and Empress).
In China (Tong), a document intended to convey orders of princes was called ryo, which was introduced into Japan. In Japan, such a document for conveying orders of princes came to be called ryoji, which also include documents issued by the Grand Empress Dowager, Empress Dowager, and Empress. In and after the mid Heian period, ryoji started to cover documents issued by other imperial families (nyoin (a close female relative of the Emperor or a woman of comparable standing), Princesses, and Shoo (princes who didn't receive any proclamation to be an Imperial Prince) in addition to princes and sango.
A historically famous ryoji is 'Prince Mochihito's order' issued to justify the Genji's raising of an army during the Genpei War.
Documents that convey imperial orders include imperial decrees and rinji (the Emperor's command).