would you please take a look at an LSAT passage:
Teenagers tend to wake up around 8:00 A.M., the time when they stop releasing melatonin, and are sleepy if made to wake up earlier. Since sleepiness can impair driving ability, car accidents involving teenagers driving to school could be reduced if the school day began later than 8:00 A.M.
What exactly does "the school day" refers to? I thought a definite article designates a specific referent to the noun which follows the definite.
In what grammar or usage could I use "the" to refer to a general concept? The usage of "the" is so confusing!
Thank you very much for your help.