Senioritis is when you get to your senior year of school and you basically just mentally check out. This is your last year, so you're probably over it, you don't want to do it any more, you're ready to be done. They don't call it "the last stretch" for no reason because you're probably stretching yourself so thin to be finish everything that you need to. You are so close to the end that you can almost taste it, you are already preparing yourself for your walk across the stage to get your diploma... but then you realize there's one little problem. You're a junior. You still have to finish your junior year out and then add one more year onto that. For me, I have to finish the next month and a half, one more semester of this year, and then my senior year and I'm done. The thing about that is, it's still a long ways to go if you're already catching the 'itis.
The last two years of college have definitely flown by. I can't believe that I'm already almost done with my first semester of junior year, but there comes a point where you're just ready to be done. You want to go out and start your real-life adult career, you're ready to be a real-life adult in general! I want to be living on my own. I want to be a teacher. I want to not be stuck in classes where I'm doing pointless projects. I want to just get on with it.
It's a crazy thing, however, because everyone says that your college years are the best time of your life. Don't get me wrong, they definitely have been the best years so far, I'm just ready for the real world. Ultimately though, my advise to you -and myself- would be to cherish the time you have in college before you do enter the real world because that's it, there's no going back. Once you leave school, that's when your true adult life begins, so try to enjoy the last few years you have left before you have to start paying the bills and grown up.