harva (“rare”) se (“that”) päivä (“day”), originally used with negation of the event that happens often, as in harva se päivä, kun hän ei.. (literally “rare is the day when he doesn't...”)
harva se päivä
- (idiomatic) almost daily, quite often
Hän käy harva se päivä katsomassa äitiään.- He visits her mother almost daily.