“Text means the sensory surface of a work of art. In film it’s the images onscreen and the soundtrack of dialogue, music, and sound effects. What we see. What we hear. What people say. What people do. Subtext is the life under that surface – thoughts and feelings both known and unknown, hidden by behavior.”
From Robert McKee’s Story: Substance, Structure, Style, and the Principles of Screenwriting (It Books/Harper Collins, 1997).