The letter "e" is the fifth letter of the English alphabet and is the most commonly used letter in the language. It appears in many words, such as elephant, energy, and example. Its shape is simple, consisting of three horizontal lines and one vertical line, making it easy to write and recognize. In mathematics, "e" also represents a special number known as Euler's number, approximately equal to 2.718. This number is important in various fields, including calculus and finance, because it helps describe growth and decay processes. For instance, it is used in calculating compound interest and in exponential functions.