vitamin D2

Synonym of リボフラビン (ribofurabin, “riboflavin”); vitamin B2

2.5D / (by extension, fandom slang) belonging to a grey area between "2D" (anime, etc.) and "3D" (live-action, etc.), such as voice actors

all day

one day, 24 hours / the daytime, the period from dawn until dusk / (figuratively) a short period of time / one day, someday, an unspecified day / the first day of the month

a birthday

regular day off (e.g. closed every Monday)

the twentieth day of the month / twenty days / Short for 二十日鼠 (hatsuka nezumi): a house mouse

幾日も幾日も: day after day

(Internet slang) A member of the online 2channel community.