“Demand for anything at a given price is the amount of it which will be bought per unit of time at that price.”
“By demand we mean the various quantities of a given commodity or service which the consumers would buy in a market in a given period of time at various prices or at various incomes or at various prices of related goods.”
The demand schedule is a table which shows the relationship between various amount of commodity demanded at various prices, while other things such as tastes, incomes, size of family etc which can affect the demand remains constant.
Demand curve is the graphical representation of demand schedule. That is, demand curve is a curve on a graph which shows the relationship of demands and prices of a commodity.