In ROBLOX, a mesh is a 3D object, such as a hat (catalog item), gear (catalog item) or 
Part. Every hat, gear, and package (except for the Mysterious Object) is made up of one or more meshes.
There are 
SpecialMeshes, which contain 
BlockMeshes and 
CylinderMeshes.
Other Mesh Variations
BlockMesh
BlockMeshes can be used as a replacement for a Part. The main difference is that a BlockMesh has pointy edges and is smooth instead of studded, welded, yielded, or glued.
CylinderMesh
CylinderMeshes, like BlockMeshes, replace what a Part looks like. A CylinderMesh is similar to but distinct from the SpecialMesh MeshType Cylinder, although they look identical.
This is now deprecated, as the cylinder mesh from SpecialMeshes is favored.
User meshes
An example of a custom mesh.
An example of forced meshing in 2014.
From 2008 to 2010, players could upload their own custom meshes via a simple exploit made public by Gamer3D. However, the user-made meshes could only be seen by placing the mesh in a game while in Roblox Studio. In early 2011, this feature was removed due to some "inappropriate content". Because of this, many users have formed groups demanding meshes to be returned as an official feature.[1]
In 2014, a user named hunte922 was able to upload meshes, with some being of Sonic heads, Portal meshes, Halo meshes and even SCP-173 from the SCP wiki. This was later removed by an Administrator named tobotrobot.
On June 9, 2016, player meshes were brought back into Roblox Studio. This caused a new section to be included in the Library section of the website dedicated to user-created meshes. This is the first time users can create meshes without the use of exploits. A mesh is required to be an OBJ or FBX file and limited to 100,000,00,000 polygons or lower to be imported.
Multi-mesh model imported as single mesh, compared to to the same model imported in bulk
On January 1, 2019, a Bulk Import feature was added in which Roblox Studio would automatically split multi-msh files into separate meshes.[2] This allows complex 3D models to preserve detail without having to deliberately lower the polygon count, and prevents the issue of the UV mapping glitching if a multi-mesh model is imported as a single mesh. Before this feature, users would separate meshes in a model with a 3D editing program, import each mesh separtely, and arrange the meshes manually back together in Roblox Studio.
Trivia
This section is a trivia section. Please relocate any relevant information into other sections of the article.
- Roblox creates their meshes on Autodesk 3DS MAX.[citation needed]