What is "proglas"

Proglas ( Old Church Slavonic Glagolitic ⰒⰓⰑⰃⰎⰀⰔⰟ, Cyrillic Прогласъ; meaning Foreword) is the foreword to the Old Church Slavonic translation of the four Gospels. It was written by Saint Cyril in 863-867 in Great Moravia (present day Moravia and Slovakia). Proglas is considered to be the first poem in literary Old Church Slavonic.