The official name of the British television programme is Dragons' Den, with an apostrophe after the word Dragons.
The title refers to the group of investors who sit on the panel and assess entrepreneurs seeking finance. In ordinary speech, the programme is often written as Dragon's Den, but the BBC programme title uses the plural possessive form because the den belongs to the Dragons collectively.
This punctuation difference is a common source of confusion, especially because international versions use different titles. The American adaptation is called Shark Tank, while other countries have used titles translated from their own versions of the format. The British spelling remains Dragons' Den.
The programme's title also explains its visual identity: entrepreneurs enter a room dominated by experienced investors and must defend their valuation, sales figures and proposed equity deal. A successful pitch may lead to an offer, but an offer is not necessarily completed after filming.