What is the medical definition of appropriate facial expression?

An "appropriate facial expression" is a look on the face that makes sense in the context of the conversation. For instance, if a woman at her postpartum exam says, "I'm very happy to have a newborn," but is tearful or unsmiling, it could be a sign of postpartum depression. Patients with Parkinson's disease sometimes have trouble showing emotion on their faces, and so their expression may not be appropriate.