Senior slump is not only a time of the year--that is, the second semester of senior year in high school--it is a state of being.
Though many students enter senior year with the intention of not falling into this intellectual rut, unless you are freakishly abnormal, you, too, will find yourself dragged into an overpowering state of lethargy. Unable to do any sort of work outside of school, you will become a master of procrastination. Personal hygiene will become irrelevant as you go for weeks without shaving, not even bothering to change out of your pyjamas in the morning. And do not even bother trying to wake yourself until at least an hour after your alarm has gone off.
Do not expect this affliction to come during the prescribed second semester, for you will be quite alarmed when, after your first quarter grades are out, you discover yourself victim to the aforementioned disease.
And above all, do not fight senior slump, lest you pass through senior year in a state of self-loathing.