If there is a flat line on a distance-time graph, it means the object is not moving or is at rest.

Here's why:

* Distance-time graphs: These graphs show how the distance of an object changes over time.

* Flat line: A flat line indicates that the distance is not changing.

* No change in distance = no movement: Since the object's distance isn't increasing or decreasing, it must be stationary.

Let me know if you have any other questions about graphs!