Definition of epic (from the 10th edition of M. H. Abrams and Geoffrey Galt Harpham’s A Glossary of Literary Terms, Wadsworth Cengage, 2012):

"In its strict sense the term epic or heroic poem is applied to a work that meets at least the following criteria: it is a long narrative poem on a serious subject, told in a formal and elevated style, and centered on a heroic or quasi-divine figure on whose actions depends the fate of a tribe, a nation,  . . . or the human race" (107).

Abram and Harpham identify the following primary features as characteristic of the epic, which they note as becoming traditional from others following Homer's Odyssey and Iliad as models:

"1) The hero is a figure of great national or even cosmic importance. . . . In Paradise Lost [e.g.], Adam represents the entire human race, or if we regard Christ as the hero, He is both God and man. . . .

2) The setting of the poem is ample in scale, and may be worldwide, or even larger. Odysseus wanders over the Mediterranean basin (the whole of the world known to Homer), and in Book XI he descends into the underworld. . . .

3) The action involves superhuman deeds in battle . . . or a long and arduous journey intrepidly accomplished, such as the wanderings of Odysseus on his way back to his homeland, despite the opposition of some of the gods. . . .

4) In these great actions the gods and other supernatural beings take an interest or an active part—the Olympian gods in Homer, [e.g.]. . . . These supernatural agents were in the Neoclassic Age called the machinery, in the sense that they were part of the literary contrivances of the epic.

5) An epic poem is a ceremonial performance, and is narrated in a ceremonial style which is deliberately distanced from ordinary speech and proportioned to the grandeur and formality of the heroic subject and epic architecture" (108).

Be on the lookout for the following epic conventions in your reading of The Iliad or The Odyssey:

• the invocation of the muse, the calling upon celestial aid for poetic inspiration,
  
  
• the beginning of the action in medias res, or "in the middle of things" as the action is joined immediately, with full explanation and elaboration coming later,
  
  
• epic similes: extended and highly elaborate "like," "as," or "so" figurative comparisons, and
  
  
• catalogues of warriors, ships, armaments, etc.