What is a great demand

If you mean supply and demand, then

supply: how much of something you have

demand: how much people want it

so if the supply is high (there are alot of product) and demand is low (not many people want it), then the prices are usually low, but

exg gassoline

so there is a limited supply in the world so the supply is low, but the demand is high (many people need gas) so the prices are high

so gas is on of them