Of the three basic communication codes, which one refers to all intentional and unintentional means, other than writing and speaking, by which a person sends a message, including gestures, appearance, posture and so forth?

The answer is nonverbal communication.

Explanation:

Nonverbal communication gives nuance to the speaker's words, and thus it's possible to assume different meanings. This includes all sorts of body language such as gesture and posture.

Some deeper layers of meaning, such as sarcarsm, use nonverbal communication (e. g. eye rolling and other facial expressions).