A geometric shape with three sides is known as a triangle. Triangles are one of the fundamental shapes in geometry and can take various forms, such as equilateral (all sides equal), isosceles (two sides equal), and scalene (all sides of different lengths). The angles of a triangle always sum up to 180 degrees, making them crucial in various fields, including architecture, engineering, and art. Triangles also serve as the building blocks for more complex shapes and structures in mathematics and design.