Dynamic demand is a way of using electricity more efficiently. It works by helping people adjust the amount of electricity they use in response to changes in the cost of electricity, or in response to changes in the demand for electricity.
So let's say it's a hot day, and lots of people are turning on their air conditioning so they can stay cool. All of those air conditioners need electricity and this increases the demand for electricity. With dynamic demand, the electricity company will increase the cost of electricity a little bit in order to get people to use less electricity and balance out the increase in demand for electricity.
When the cost of electricity goes up, the people using electricity can adjust the amount of power they use in order to still get what they need without the cost being too high. This helps to keep the electricity system balanced and working properly.