Woven wire mesh
Woven wire mesh is made through a woven process in which the weft wire (width wire) is thread through the warp wire (length wire) and continuing this process produces the mesh that is called woven wire mesh.
Warp Wire – All wires running lengthwise of the cloth as woven.
Weft Wire – All wires running across the cloth as woven.

Welded wire mesh:
“Welded mesh” is an electric fusion welded prefabricated joined grid consisting of a series of parallel longitudinal wires with accurate spacing welded to cross wires at the required spacing. This type of mesh is a square grid of uniformly placed wires, welded at all intersections, and meeting the requirements.

Plain woven wire mesh

Crimped woven wire mesh
Twilled weave woven wire mesh
Plain Dutch weave mesh (Hollander mesh)
Twill Dutch weave mesh
Reverse Dutch weave mesh

In one linear inch, the number of linear holes that in the woven mesh is the mesh number.
This is an example of 4 MESH 

The space between, one wire and the second wire is the aperture for the mesh. 

The ratio of the area of the aperture to the area of the mesh expressed as a percentage is the open area for the mesh.
Percentage Open Area  example calculation for Mesh 6 wire dia (D=0.9mm) Aperture (A=3.33mm)
The mesh has a 62% open area

Metal sheets are punched out through a punching machine and it gives holes on the sheet which makes it perforated metal mesh. During the punching process, metal has been removed to make perforated metal.

Expanded metal mesh is produced through cutting, expanding, and making a hole in the metal sheet.