The number "3.14159" is an approximation of the mathematical constant known as π (pi). This constant represents the ratio of a circle's circumference to its diameter, meaning that for any circle, if you divide the circumference by the diameter, you will always get approximately 3.14159. π is an irrational number, which means it cannot be expressed as a simple fraction and its decimal representation goes on infinitely without repeating. It is widely used in mathematics, engineering, and physics, particularly in calculations involving circles and circular shapes.