'2D' stands for 2-dimensional. A 2D shape is any shape that has two dimensions. Think about what it means to have two dimensions for a moment. If we had only one dimension to work with, we could only move backwards or forwards in a line. A line is one-dimensional. If we had two dimensions, on the other hand, we could go forwards and backwards in a line and turn in any direction to start a new line. We are essentially able to travel anywhere on a flat surface. In mathematics, a flat surface is called a plane. A plane is one example of a two-dimensional shape. A plane is essentially the largest sheet of paper you will ever find. In fact, it is a sheet of paper so large that it never ends. One way of thinking about 2D shapes is anything that lays flat on a piece of paper.
Any n-sided figure, which can be perfectly and wholly traced on a plane is a 2D figure or polygon. This means any figure having all points on a single plane is a planar figure. Some examples are
### Rectangle
Number of sides - 4
Special Info-
Has four sides, with opposite sides parallel and adjacent sides of same or unequal length(a and b)
All internal angles are 90 degrees
Sum of all internal angles in 360 degrees
Diagonals are mutually perpendicular and bisect one another