Mesh aperture
The mesh aperture of a mesh fence is the size of the hole between the wires.
Usually, higher security fencing has mesh with a smaller aperture, because it is harder to climb and to cut with hand tools. This is sometimes known as anti cut and anti climb mesh.
Some examples of fences with small mesh apertures are 358 welded mesh panels and chain link mini mesh.
You can also choose mesh with a larger aperture to save money on a fence. Because there is less steel used to make mesh with larger apertures, it's usually cheaper.