The intersection of two planes is called a line.
When two planes intersect in three-dimensional space, they do so along a straight line. This is because, theoretically, two planes can either be parallel (in which case they do not intersect) or they intersect at a line where each point on this line is part of both planes. The properties of this intersection are important in various fields like geometry, physics, and computer graphics, as they can help in understanding spatial relationships and solving problems related to three-dimensional models.