When the majority of aircraft finish the flying for the day around the same time...generally around 1700L, and the crews write up maintanence issues. As result, many trips for the following day are put back in the uncovered file resulting in a 5 o'clock flush.
Boss, "Why do we have 12 trips for tomorrow still uncovered?"

Scheduler, " We just had 7 aircraft all finish their day and the crews wrote up their aircraft."

Boss, "Ahh, the 5 o'clock flush".
by Not A Mechanic August 5, 2011
Get the 5 o'clock flush mug.