Epic convention refers to the traditional features and techniques used in epic poetry to convey grand themes and narratives, such as invoking a muse, beginning in medias res, and employing elevated language. These conventions establish the epic's larger-than-life quality, helping to depict heroic deeds and significant events within a culture. In the context of works like 'Paradise Lost', these conventions contribute to the poem's exploration of themes such as free will, obedience, and the nature of good and evil.