Demand is quantity of a good buyer who wishes to purchase at each conceivable price.
The law of demand explains us that if the price of certain commodity increases, its quantity demanded will automatically decrease and vice-versa.
A demand schedule is the table which shows various combinations of the quantity demanded and the price.
A demand function is an equational representation of the demand as a function of its number of determinants.
A demand curve is the graph which obtains when the price is plotted against the quantity demanded.
Shifts in demand curve plotted in P-Qd space and are caused by the changes in any determinant of the demand other than price of the good/commodity itself.
Movements along the curve correspond to alterations in the variable on vertical axis.