Final answer:
A differential equation is an equation that relates functions and their derivatives. It is often studied after calculus and is used to model and solve problems involving changing quantities and their rates of change.
Step-by-step explanation:
A differential equation is an equation that relates functions and their derivatives. It is a subject often studied after calculus within a mathematics curriculum. Differential equations are used in various fields, including physics and engineering, to model and solve problems involving changing quantities and their rates of change.