Geometry is the study of shapes, sizes, and spatial relationships. Two-dimensional shapes have length and width. Three-dimensional shapes also have depth.

Perimeter is the distance around a shape. For a rectangle, P = 2(length + width). Area is the space inside a shape. For a rectangle, A = length × width. For a triangle, A = ½ × base × height. For a circle, A = π × r².

Volume measures the space inside a 3D shape. For a rectangular prism (box), V = length × width × height. For a cylinder, V = π × r² × height.

Angles are measured in degrees. A right angle is 90°, a straight angle is 180°, and a full rotation is 360°. The angles in any triangle always add up to 180°.