Indentation refers to the shape in which a part of a graphic is concave inward. Correspondingly, convex refers to the shape in which a certain part of the figure protrudes outward. The shape of the concave surface can be varied, such as the concave angle inside the polygon, the concave arc inside the circle, the notch inside the glyph and so on.
Concave surfaces play an important role in graphic recognition, understanding and design. These concave surfaces may appear in different geometric shapes, design elements or artistic expressions.