👉 In mathematics, a "focoid" is a geometric shape that resembles an inverted equilateral triangle. It is named after its resemblance to a focal point or focus in an optical system. These shapes are often used in optics and physics, particularly for calculating the focal length of lenses and mirrors. Focoids can be found in many natural phenomena such as the sun's rays hitting the Earth, reflecting off surfaces, and even on the surface of water.
