Close body contact where ranged strikes stop working. A defensive tool in boxing, an entire discipline in Muay Thai.
In boxing the clinch breaks your opponent's rhythm and buys a breath — the referee then separates you. In Muay Thai it isn't an escape hatch but a core phase of the fight with its own technique: the plum grip behind the neck controls your opponent's head and posture while you work with knees. The key departure from instinct is that you don't pull with your arms in the clinch, you control through posture and hips — arms alone fatigue in seconds. For beginners: head against your opponent's shoulder or chest, elbows tight, back straight. Lift your head and round your back and you'll be pulled off balance and lose the position.