'Demand' in this case refers to some need or desire to buy something. If many people want to buy a certain type of car and there aren't many produced yet, we would say that there is not enough to meet demand - the demand of the public. The amount of electricity required by an area would be demand. The amount of electricity at the busiest time of the day would be peak demand. So we could talk about having enough electricity to meet the demand.

This is closely related to economics. When a country can't meet the demand of its people, it will be met elsewhere, i.e by importing it from another country. For example some years ago Indonesia imported soy beans from another country because it couldn't meet the demand of soy beans by itself. At that time Indonesia couldn't produce enough soy beans for its people. To meet someone's demand means to provide for someone's need.