PLANES!!!! 

Definition of a plane: A surface such that if any two points on the surface are connected by a line, all points on the line are also on the surface.

Figure A is a plane.

These are two perpendicular planes below.                Here are two parallel planes below. 

                           

 

The Four Ways That Determine A Plane

1 Three noncollinear points determine a point.
2 A line and a point not on that line determine a plane.
3 Two parallel lines determine a plane.
4 Two intersecting lines determine a plane.

  BEEF