Step 1: Understanding the Concept: 
Mass communication refers to the process of creating, sending, receiving, and analyzing messages to large audiences via verbal and written media. Its key characteristic is its ability to reach a large, anonymous, and heterogeneous audience simultaneously. Communication that is personal and directed at a specific individual or a small group is known as interpersonal communication. 
Step 2: Detailed Explanation: 
Let's analyze the options: 
1. Cinema: Films are shown to large audiences in theaters, making cinema a form of mass communication. 
2. Radio: Radio broadcasts signals over a wide area, reaching thousands or millions of listeners at once. It is a classic example of mass communication. 
3. Letters: Letters are a form of written communication typically addressed to a specific person or a few known individuals. This is an example of interpersonal communication, not mass communication. 
4. Newspapers: Newspapers are printed in large quantities and distributed to a wide readership, disseminating information to the masses. It is a primary form of mass communication. 
Step 3: Final Answer: 
Letters are a form of personal communication and not an example of mass communication.