Expression implies a revelation about the characteristics of a person, a message about something internal to the expresser. In the context of the face and nonverbal communication, expression usually implies a change of a visual pattern over time, but as a static painting can express a mood or capture a sentiment, so too the face can express relatively static characteristics (sometimes called physiognomy). The concept of facial expression, thus, includes:
1. a characteristic of a person that is represented, i.e., the signified;
2. a visual configuration that represents this characteristic, i.e., the signifier;
3. the physical basis of this appearance, or sign vehicle, e.g., the skin, muscle movements, fat, wrinkles, lines, blemishes, etc.; and
4. typically, some person or other perceiver that perceives and interprets the signs.
Facial expressions are an important channel of nonverbal communication. Many animal species display facial expressions, but expressions are highly developed particularly in the primates, and perhaps most of all, in humans. Even though the human species has acquired the powerful capabilities of a verbal language, the role of facial expressions in person-to-person interactions remains substantial. Messages of the face that provide commentary and illustration about verbal communications are significant in themselves. To see examples of such nonverbal communication, see the FAQ. Other types of expressions provide another, different mode for understanding the private, hidden side of the inner person, a side which may not be accessible in the form of verbalizations. For example, the facial behaviors related to emotion can reveal part of the feeling side of a person's private life. Such emotion indicators range from stereotyped, full-face expressions that are obvious to fleeting, partial-face movements that are hard to see.
The videos below are about facial expressions! I hope you enjoy them!