Ah, the epic. The most exalted, fancypants of all genres, the epic is a kind of narrative poem that dates back to ancient Greece and the classical period. Homer and other likeminded bros used the epic to tell stories about larger-than-life heroes and their triumphs on and off the battlefield.
Epics usually involve supernatural or mythic elements like gods who like to meddle in human affairs. They are written in an elevated style and use lots of long similes, called heroic similes. Other conventions include an invocation to the muses and starting in medias res, a Greek phrase that means "in the middle of the action."
Homer wrote two main epics: the Iliad and the Odyssey. After him, Virgil, a Roman guy—ahem, the Roman guy—wrote the Aeneid. Check out our analysis of epic in the Odyssey for some ideas on how to spot one.