Final answer:
A pen picture consists of three lines that are each a complete subject, describing someone or something in a concise and evocative way.
Step-by-step explanation:
In a pen picture, each of the three lines is a complete subject. This type of description, often used in writing exercises, allows for a brief and intense characterization of a person, place, or thing in just a few well-chosen lines or sentences. The term 'pen picture' suggests a sketch made with words instead of actual visual elements, designed to give a quick but memorable impression.