The mathematical constant that approximately equals 3.14 is pi (π). Pi is the ratio of the circumference of a circle to its diameter and is an irrational number, meaning it has an infinite number of non-repeating decimal places. It is widely used in various fields of science, mathematics, and engineering, particularly in calculations involving circles, spheres, and periodic functions. The value of pi is crucial in trigonometry, geometry, and many formulas in physics, contributing to its pervasive significance across disciplines.