4D space-time is explained as a combination of three spatial coordinates (x, y, z) and one temporal coordinate (t), forming an "event" that represents a point in space at a specific time. The collection of all such events is referred to as "spacetime." An example illustrates this concept by describing an appointment that requires knowing the location of the office in three dimensions and the time of the appointment. While some participants seek further examples, the discussion emphasizes the clarity of the initial explanation. Overall, the conversation highlights the simplicity of understanding 4D space-time through relatable scenarios.