An epic nap is any nap which begins as an intended 15-minute to one-hour venture and ends as a 5- to 8-hour excursion through the valleys and mountains of the realm of sleep.
Additionally, if you have two major events scheduled in a day, and you take a nap between the two, causing you to miss the second of said events, this nap may qualify as an epic nap.
Finally, if you make plans with friends, but decide to take a nap before you go out, and then end up sleeping for an eight- or nine-hour period during which none of your friends can reach you and may begin to presume you dead, this may also qualify as an epic nap.
"Man, I was so tired after my final. I went home to take a nap, right? Fell asleep at 1, meant to wake up at 2, but ended up sleeping until 9! Epic nap."
"Man, I was so tired after my first final. I went to the library to get a nap before my second one, but I ended up sleeping through it! A custodian woke me up when they were closing the building. Epic nap."
"Nikki said she was going to go to the movies with us, but none of us could reach her. We started to worry that she might be dead or something, but it turned out she was just taking an epic nap."