Illustrated · 1 min
Planes are flat cross-sections of space
Planes are just two-dimensional spaces! Any 2-D graph you see (a graph with just an and a axis) represents one plane. You can think of pieces of paper as representing a plane, too!
Image Source: David Eppstein [Public domain], via Wikimedia Commons
The image above shows two planes that cross through each other. The image below should be familiar—it's just the axes for a graph! The image below represents a plane, too.
A plane can be defined by three points: the two points that define a line, and a point to define which direction the plane extends in the second dimension.