Final answer:
A plane is a two-dimensional flat figure, and the intersection of two non-coincident planes is a line.
Step-by-step explanation:
A plane is a two-dimensional flat figure that extends infinitely in all directions. It is defined by any three non-collinear points or by a line and a point not on that line.
The intersection of two planes that do not coincide (if it exists) is a line. This line is formed by the points where the two planes intersect.