Base e, also known as Euler's number, is a mathematical constant approximately equal to 2.71828. It is the base of the natural logarithm and is widely used in various fields such as mathematics, physics, and finance. Base e is an irrational number, meaning it cannot be expressed as a simple fraction, and its decimal representation goes on forever without repeating. One of the key properties of Base e is its unique relationship with exponential growth and decay. In calculus, the function e^x is notable because its derivative is the same as the function itself. This property makes Base e particularly important in solving problems involving continuous growth, such as population dynamics and compound interest.