Comps: Comprehensive exams. I believe most Ph.D. programs have them, and even some masters programs, but each program does it differently and holds them at different times. For instance, some criminology programs hold them between the first and second year of classes, others hold them after classes but before dissertation, and then some others don't even have them! As you can see, there is a lot of variation so my experience with my comps are unique to my institution :)
Our comps has 3 parts: policy, theory, and research methods. The exam is held over 2 days and each part is 4 hours long. The first day you take two exams and the second day you just take one. Thankfully it is typed but it is closed book so it is a huge exercise in understanding, synthesizing, and memorizing a large body of knowledge.
In order to prep, we are told to 'know everything' in the field. That is why I have started prep work now, more than 6 months out. I am planning on doing a large amount of reading articles and books then consolidating all of that information into outlines and flashcards as that is what works best for me.
Students take the semester 'off' that they're sitting in order to study full time and that is my plan. I will still be working as a teaching/research assistant but instead of taking classes this fall, I will be studying. From what I've gathered, this is very much a mental game and is a marathon of sorts. The stress and other emotions you experience can run the gamut but that's what we signed up for to get our doctorate I guess!
So that is a not-so-brief overview of my comprehensive exams. As it is about to be one of the few things going on in my life, I would imagine you