It is a poem that is (a) a long narrative about a serious subject, (b) told in an elevated style of language, (c) focused on the exploits of a hero or demi-god who represents the cultural values of a race, nation, or religious group (d) in which the hero's success or failure will determine the fate of that people or nation. Usually, the epic has (e) a vast setting, and covers a wide geographic area, (f) it contains superhuman feats of strength or military prowess, and gods or supernatural beings frequently take part in the action. The poem begins with (g) the invocation of a muse to inspire the poet and, (h) the narrative starts in medias res (see above). (i) The epic contains long catalogs of heroes or important characters, focusing on highborn kings and great warriors rather than peasants and commoners.
Example: Beowulf is an epic poem. long narrative about a serious subject, focused on BEowulf's heroic exploits, his success or failure in fighting dragons will determine future of the GEats. Focuses on kings and warriors, not peasants.