A "90-degree" angle is formed when two lines meet at a right angle, creating a quarter of a full circle. This angle measures exactly 90 degrees, which is a standard reference in geometry. It is commonly represented by a small square in the corner of the angle, indicating that it is a right angle. In everyday life, 90-degree angles are found in various objects and structures, such as the corners of a square or rectangle. They are essential in construction, design, and carpentry, ensuring that walls and surfaces are straight and properly aligned.