The number "base e," approximately equal to 2.71828, is a mathematical constant that serves as the foundation for natural logarithms. It is an irrational number, meaning it cannot be expressed as a simple fraction. Base e is widely used in calculus, particularly in problems involving growth and decay, such as population growth and radioactive decay. In addition to its applications in calculus, base e appears in various fields, including finance and statistics. For example, it is used in the formula for continuous compound interest, where the growth of an investment is calculated over time. This makes base e essential for understanding exponential functions and their real-world implications.