(追記) (追記ここまで)
Two
Dimensions
Two Dimensional
The property of a plane that indicates that motion can take place in two perpendicular directions.
Formally, saying a plane has only two dimensions means that you can find two vectors in the plane for which neither is a multiple of the other. In addition, for any set of three vectors in the plane, one of them can be written as a linear combination of the other two.
See also
Zero dimensions, one dimension, three dimensions, n dimensions