Noun
(chiefly US, idiomatic) The week during which new members are required to undergo undignified rites of initiation or gruelling discipline in order to be accepted into a fraternity, sorority, secret society, military group, etc.
(chiefly US) In a college or university, the week leading up to final examinations.
Hell Week (plural Hell Weeks)
Alternative form of hell week
Classes go live at midday exactly a week in advance, and during a Hell Week the good spots get booked up fast. Source: Internet