铁三角 literally means 'iron triangle' but is a culturally loaded term with several specialized senses. In political science and sociology it describes a mutually beneficial, stable power structure among three parties (e.g., government, military, and business). In the consumer electronics world it's the common Chinese name for Audio-Technica, a major audio equipment brand. Colloquially, it refers to an inseparable trio of close friends or allies. The literal meaning of a physical triangle made of iron also exists but is rare.