Plane

A plane is a flat, level surface which may be sloping at a particular angle.
1) A surface in which if any two points are chosen a straight line joining them lies wholly in that surface.
2) A flat or level surface.
3) A level of existence, consciousness, or development on the intellectual plane.

In mathematics, a plane is a flat, two-dimensional surface that extends infinitely far. A plane is the two-dimensional analogue of a point (zero dimensions), a line (one dimension) and three-dimensional space. Planes can arise as subspaces of some higher-dimensional space, as with one of a room's walls, infinitely extended, or they may enjoy an independent existence in their own right, as in the setting of Euclidean geometry.

Sources:

Англійський словник Коллінза, електронний ресурс: https://www.collinsdictionary.com/

Словник Webster's Dictionary https://www.merriam-webster.com/

Anton, Howard (1994), Elementary Linear Algebra (7th ed.), John Wiley & Sons, ISBN 0-471-58742-7.