Direct Answer: A boundary governs your own actions: it dictates what you will do in a given situation to preserve your well-being. Control dictates someone else's actions: it demands that they change their behavior, friends, or clothes under the threat of punishment. Boundaries preserve personal freedom; control restricts it.
If you are unsure whether a statement or behavior is a boundary or an attempt to control, use this comparative guide to evaluate the core intent and focus.
In modern relationships, people sometimes use the word 'boundary' to mask control. Stating: 'My boundary is that you cannot talk to other men' is not a boundary—it is a rule imposed on another. A healthy boundary is: 'I will not remain in a relationship where flirting with others is standard behavior, and I will leave if it happens.' One restricts your partner's autonomy; the other maintains yours.