What is the intersection of two planes?
If there are two unique, non-parallel planes in space, they will intersect, and their intersection will be a line.
Yes. A line can be the intersection of two planes, or any number of planes. A real-world example would be the central axis (axle) of a paddlewheel on a steamboat, which would be coplanar with all of the planes represented by the individual paddles. A single line is similarly the intersection of perpendicular planes.