Euler's Number, denoted as e, is a mathematical constant approximately equal to 2.71828. It is the base of the natural logarithm and plays a crucial role in various areas of mathematics, particularly in calculus. e arises naturally in problems involving growth and decay, such as population growth and radioactive decay. The significance of e extends beyond pure mathematics; it is used in fields like finance, physics, and engineering. For example, in compound interest calculations, e helps determine the growth of investments over time. Its unique properties make it essential for understanding exponential functions and their applications.