Another way to state it is the foreground is what is between your point of focus (PoF) and the camera.
In a landscape photo the point of focus may be determined by the hyper focus distance rather than being on any specific 'subject'.
The PoF is usually on the primary subject of your photo.
Point of focus is important because depth-of-field (DoF) extends some distance both in front of the PoF (foreground)and behind the DoF (background).
How far in front of and behind the PoF the DoF extends is variable by controlling the PoF distance, the lens focal length, the lens aperture and how far behind the PoF the background is.
For example - If we want to photograph a person but want the background blurred we have to make sure the person is well in front of that background and that the person fills the frame so the PoF is close enough to the camera to make the DoF sufficiently shallow that the background IS blurred.