Individual Demand

Individual demand is the demand curve of one individual or firm. By using the theory of preferences we can derive the individual demand curve. The consumer’s budget line can change because of changes in prices or because of changes in income. Here, we will assume that the preferences themselves do not change. This makes us able to derive both the demand curve and the so-called Engel curve, which shows how demand depends on income. 

Also see:

The Individual Demand Curve
The Engel Curve
Market Demand