What is "idiomelon"

Idiomelon ( Medieval Greek: ἰδιόμελον from idio-, "unique" and -melon, "melody"; Church Slavonic: самогласенъ, samoglasen)—pl. idiomela—is a type of sticheron found in the liturgical books used in the Eastern Orthodox Church, the Eastern Catholic Churches which follow the Byzantine Rite, and many other Orthodox communities like Old Believers. Idiomela are unique compositions, while avtomela or aftomela—sing. automelon, avtomelon or aftomelon ( Medieval Greek: αὐτόμελον, Church Slavonic: самоподобенъ, samopodoben) were used to create other hymns by a composition over the avtomelon's melody and following the poetic meter provided by the musical rhythm—this genre was characterised as prosomoion or prosomeion ( Medieval Greek: προσόμοιον "similar to", Church Slavonic: подобенъ, podoben).