I heard our universe is flat. Then one question is puzzling in my mind. If our universe is really flat, why we measure distance from any point across in a spherical way. In other words, why we say, the comoving distance (radius) is now about 46.6 billion light years. If this radius is only treated for observable universe, then how does science find that the universe is flat knowing nothing beyond the limit of the universe.
There are some questions in SO, however, they do not assimilate what I intended to know. In this question, for instance, OP asked about whats the shape of the universe. And also there are some terms related to black holes, 3D shape, ball etc. Apart from those complexity, my intention is simply to be clarified, why we call our universe flat? And by word flat, what I meant "having a level surface; without raised areas or indentations". Am i missing any alrernative meaning of flat here?