A plane figure is a flat, two-dimensional shape that can be drawn on a flat surface, like a piece of paper. These figures are defined by their boundaries, which can be straight or curved lines. Common examples of plane figures include triangles, squares, circles, and rectangles. Plane figures can be classified based on their properties, such as the number of sides or angles they have. For instance, a triangle has three sides, while a rectangle has four sides and right angles. Understanding plane figures is essential in geometry, as they form the basis for more complex shapes and concepts.