For a given line \(l\) and point \(P\), if we draw a line through \(P\) perpendicular to \(l\), then this line will intersect \(l\) at a point \(Q\). The point \(Q\) is called the *foot of the perpendicular line*.

Similarly, if we draw an altitude of a triangle or another figure, the point where the altitude meets the side to which it is perpendicular is called the *foot of the altitude*.