Rule of Space
The guideline that a subject which is moving or looking in a direction should have space in front of it within the frame.
In depth
Space ahead of a subject reads as possibility and destination; space behind reads as constraint. Because the eye follows a gaze or a direction of travel, denying it somewhere to go creates tension against the frame edge — which is exactly why breaking the rule deliberately is a way to make a picture feel uncomfortable.
Examples in practice
A cyclist placed on the left of the frame moving right feels natural; crowded against the right edge, the picture feels trapped.