Vanishing Point
The point in an image at which receding parallel lines appear to meet.
In depth
The vanishing point sits on the horizon line at the viewer's eye level, which is why its position in the frame reveals exactly how high the camera was held. Placing it centrally gives a formal, symmetrical picture; moving it off-centre creates a more dynamic one. A scene can have several, one for each set of parallels.
Examples in practice
A corridor shot dead on has its vanishing point at the centre; shot from one side it moves toward the frame edge.