Demand registration is the right that lets preferred stockholders compel the company to file an SEC registration statement enabling public sale of their shares. It is typically exercisable after a 180-360 day post-IPO waiting period, limited to 1-3 demands per investor group, subject to $5M-$10M minimum offering size, and accompanied by company expense coverage. It is the most significant registration right structurally because it gives investors the affirmative ability to force a registration on their own initiative, rather than waiting for the company to act.
The mechanic of a demand registration: