Documented: 間, ma or aida, depicts light (sun in the modern form, moon in the older) seen through a gate or doorway, meaning between, interval, room, timing. The kanji network notes the older form showed moonlight through the door's crack, later changed to sun. The word covers spatial gap, temporal pause, and the room you are standing in.
The documented canonization: architect Arata Isozaki's Ma: Space-Time in Japan exhibition (Paris, 1978, then New York and Tokyo) presented ma as the unified theory of Japanese art, the interval in music, the pause in theater, the emptiness in a tokonoma alcove, and fixed the term in global design vocabulary. Before Isozaki it was a word; after, a doctrine.
The use reading: ma is why the shakuhachi phrase is mostly silence, why sumi-e leaves the silk bare, why the tea room's scroll alcove is empty until one flower enters it. Critics note the concept can harden into a nationalist cliché, Japan as the land of tasteful absence, but the practice underneath is real craft: arranging nothing until it holds.
Is the interval empty, or is the interval the content?