The term epic is overused today to mean something big or grand. In literature it refers to a specific type of hero story. In the an epic, an epic hero has to do certain things, such as:
1. Influence a large group of people (country, culture, kingdom).
2. Travel to an underworld.
3. Interact with the supernatural.
4. Go on a journey.
5. Complete superhuman challenges/ overcome obstacles.
6. Return home.
It is clear that Milton in one sense is following directly in the footsteps of the writers of other epic classics, such as Homer, in the way that he mirrors so many of the conventions of epic authors. For example, he starts the poem in the middle of the story, just after the conflict between Satan and God that has seen Satan and his forces cast down into hell. In the same way, he invokes the aid of the Muse to help him write his words as he seeks to "justify the ways of God to men." However, at the same time, in addition to including some of the traditional aspects of the epic in his work, it is clear that Milton goes above and beyond, taking the epic as a literary form and pushing the boundaries in what he hopes to do with it, as this appeal to the Muse (the Holy Spirit) makes clear:
...what in me is dark
Illumine, what is low raise and support;
That to the height of this great argument
I may assert eternal providence,
And justify the ways of God to men.
There is a sense in which Milton states in all humility that his goal is to to what no other man has achieved before: show God's wisdom and planning to a mortal audience as he strives to achieve "Things unattempted yet in prose or rhyme." This is a radical departure from the epic classics before Milton as he deliberately extends the remit of the epic in order to achieve his aims that smack of pure hubris, yet are expressed in all humility. Milton then deliberately situates his work in the genre of the epic, copying a number of different aspects in order to clearly identify his work as an epic but also to then challenge that genre.