A Square has 4 edges, all the same length.
All its vertices (corners) are right-angled.
It has 2 diagonals, both the same length.
It has 4 lines of symmetry, and rotational symmetry of order 4
With this shape it is only necessary to know one of its dimensions, and all the others can be derived from that.
Where (for brevity) it says 'edge', 'perimeter' and so on, it should, more correctly, be something like 'length of edge' or 'edge-length' etc.