Final answer:
A concave profile is identified by a receding forehead and chin. It's opposite to a convex profile where these features protrude outward, and differs from a straight profile with aligned features, or a balanced profile which is proportional.
Step-by-step explanation:
A concave profile is characterized by a receding forehead and chin. When looking at the side view of a person's face, if both the forehead and chin curve inward toward the plane of the face, this indicates a concave profile. This type of facial profile can be described in contrast to other profiles, such as a convex profile where the forehead and chin tend to protrude outward, or a straight profile where the forehead, nose, and chin align in a more or less vertical plane. A balanced profile would have features that are proportionate and align harmoniously without significant recession or protrusion.