In Dragons' Den, the investors' area that entrepreneurs enter to pitch is called the Den.
The title describes the central studio space where entrepreneurs face the panel of business investors. A typical pitch begins when the entrepreneur walks into the Den, introduces the business, states the amount sought, and offers a percentage of ownership in return. The Dragons then question the entrepreneur before deciding whether to make an offer.
The word “Den” is part of the British programme’s identity and distinguishes it from versions that use different animal imagery or titles. The American adaptation, for example, is called Shark Tank, while the investors are called Sharks rather than Dragons.
The Den is not the boardroom. Although business discussions often use boardroom language, the show’s official setting and title use “Den.” That simple terminology is also why the correct answer is a short phrase rather than a name of a physical BBC studio.