The time in between Friday night, and Saturday morning. Fradurday morning is before 5:00 am because any time after that is considered Saturday morning.
A fraturday is a Saturday in which Fraternity bros get dressed in their "frattire" (polos, backwards hats, khakis, and frat flops) drink beer on the "fratio" while grilling and playing brotastic music along the lines of Oasis, Third Eye Blind, Dave Matthews, and many others
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.