Direct proportionality is a relationship between two quantities where an increase in one quantity results in a proportional increase in the other. For example, if x is directly proportional to y, then doubling x will also double y. This relationship can be expressed mathematically as y = kx, where k is a constant. In practical terms, direct proportionality can be observed in everyday situations, such as when buying fruits. If the price of apples is k dollars per pound, then buying 2 pounds will cost 2k dollars. This consistent ratio helps in predicting costs based on quantity.