The distance between a point and a plane is the measure of the segment whose extremes are the point and its orthogonal projection on the plane:

The distance between a line and a parallel plane is the distance between any point on the line and the plane:

The distance between two parallel planes is the distance between any point on either plane and the other plane:

The distance between two straight lines, **r** and **s**, is the distance between any point of one of them and the plane passing through the other and parallel to the first line: