also: セオリ
noun
Used for a systematic explanation or set of principles, similar to English 'theory'. Often appears in academic or analytical contexts.
彼のセオリーはまだ証明されていない。
His theory has not been proven yet.
noun
standard procedure; common strategy; established tactics
Refers to a widely accepted method or approach in a particular field, such as business, games, or sports. Implies a conventional or textbook way of doing things.
このゲームでは、まず中央を取るのがセオリーだ。
In this game, the standard strategy is to take the center first.