非理性 is a compound formed with the prefix 非- (non-) and 理性 (rationality), meaning 'irrational' or 'irrationality'. It is used in psychology, economics, and philosophy to describe behavior, decisions, or beliefs that are not based on reason or logic. As an adjective, it modifies nouns like 行为 (behavior) or 决策 (decision); as a noun, it refers to the concept itself. The prefix 非- is productive, so you can understand similar words like 非正式 (informal) or 非传统 (non-traditional).