In Dragons' Den, entrepreneurs usually offer equity in their business in return for investment.
Equity is an ownership share. When a founder offers a percentage of a company, the Dragon is being asked to provide money in exchange for part ownership and a possible future return. The percentage offered is therefore central to the pitch, alongside the amount requested and the company's claimed valuation.
The arrangement is different from a salary, which is payment for work, and from a simple loan, which normally must be repaid with interest. A patent may protect an invention, but it is not normally the standard consideration offered to a Dragon. A television contract is also not the purpose of the negotiation.
The exact terms vary from pitch to pitch. Dragons may reject the proposed percentage, make a different offer, or join another Dragon. Some on-screen agreements can also change or fail during later due diligence.