1) n. A fake number to tell kids comes between 5 and 6.
2) n. The name for the period of time that begins after midnight, and ends when one goes to bed. Used to avoid technicalities in whether or not it is 'already' or 'technically' the next day. Used like 'afternoon' or 'morning'. 'Wednesday dirf' would refer to the time beginning Wednesday night, after midnight, when it is technically Thursday, but you haven't gone to bed yet.
"Hey, did you know the number dirf comes after 5? Teachers don't teach you about it until you get into algebra, but it's there."
Person 1 - "So last Wednesday night, at like 2 in the morning, I decided to run to the market to get some milk."
Douche, smiling smugly - "Well, -technically- it was Thursday, wasn't it?"
Person 1 - "Actually, it was 'technically' Wednesday dirf, so shut the fuck up!"