I am working on making a gun for a future game and i need a mesh to do it but first i need to know what a mesh is.
Meshes were a previously recognized feature on ROBLOX that changed something as simple as a brick to a form of objects such as hats or gear displayed on the ROBLOX Catalog. Meshes used to be created by ROBLOX staff and users but due to innapropriate conent, ROBLOX removed meshes as a official feature for ROBLOX users. Any meshes created to this date however, are still able to be used. The ROBLOX Wiki provides a list of file meshes that have been created, and to your luck has some guns included.
Basically, a mesh is a 3D object which in ROBLOX uses as a 'virtual decal' commonly used as hats, gears, packages. They can be accessed via SpecialMesh or Hats and has no collision detection. (The parts do that) You can change the color or decal of a Mesh with a picture editor or such. It was possible to upload meshes around in 08'-10'
Basically, a mesh is a model of a 3-D object. When you spawn a brick it normally shows as a cube or a rectangular prism, but you can change it if you want. Spawning any meshes can control the scale of the brick and the offset. Messing with it won't affect the actual brick.