Originally Posted by Ronin Aquila
Pray tell, is that short for a four worded slogan? Only started to learn net slang a scant 4 months ago.
"Flag" is a term one uses for events that occur in dating sims, that functions as turning points and cross roads for different situations and endings.
Since Eri's encounter with Harima were always "dating-sim-like", in the sense that they hardly ever talk normally, but always meet at critical situations, their relationship is called the "Flag".
There are some terms I found on the Internet: Note that there is likely more out there.
Flag/Jersey Faction: Harima x Eri
Oudou (main) Faction: Harima x Tenma
Dream come True Faction: Hanai x Yakumo
Riceball Faction: Harima x Yakumo
Kids Meal Faction: Harima x Eri or Harima x Yakumo
(Little Japanese Flag + Onigiri = Japanese Kids Meal)
Monkey Faction: Harima x Eri x Yakumo
Flute Faction: Hanai x Mikoto
Chinese Food Faction: Asou x Sara
Applejuice Faction: Imadori x Ichijou
Under the Moon Faction: Hanai x Harima
Cousin Faction: Harima x Itoko
Bloody Mary Faction: Eri x Yakumo