A circle.
However, a way of showing a sperical object on a flat surface, such as a map of the world, is called a projection. The most widely used example is the "Mercator Projection", the familiar classroom World map, although there are many others.
on a flat map
Is called projection .
mercator
mercator
mercator
mercator
mercator
Its called a projection map
Its called a projection map
projection map
A flat round object is a circle. Surface area of a circle = pi*radius squared.
The flat surface that goes on and on in all directions has no boundaries. This flat surface is called infinite surface. Accordingly, the answer is that the flat surface that goes on and on in all directions is called an infinite surface.