Mesh

Introduction
In FreeCAD the word "Mesh" is normally used to refer to a Mesh MeshObject ( class), a type of object that defines 3D data but is not a solid "Shape".

Meshes are very simple objects, containing only vertices (points), edges and triangular faces. In general, they are very easy to create, modify, subdivide, and stretch, and can be passed from one application to another without any loss of detail. In addition, since meshes contain very simple data, 3D applications like animation software and video games can manage very large quantities of them without using a lot of computing resources.

However, in the field of engineering meshes present one big limitation: they are only made of surfaces, and have no "mass" information, so they don't behave like solids. This means that all solid-based operations, like boolean addition or subtraction, are difficult to perform on meshes.

See Mesh MeshObject for more information about this type of object.

How to use
Meshes are normally created by internal functions of the Mesh Workbench, or by importing mesh format files, like STL and OBJ.

Essentially, every object derived from a Mesh Feature ( class) is expected to hold and manipulate a Mesh.

Since FreeCAD is designed to be a solid modeller primarily, it is better suited to deal with solid Shapes. It can import and display Meshes in the 3D view, but to transform them or create new geometry, the Mesh first needs to be converted to a Shape. In many cases, this conversion is not automatic, and requires re-creating the geometry using solid modelling techniques, making use of Part and PartDesign tools.

Finite element meshes
The word "Mesh" is also used in the field of finite element analysis (FEA).

When an object with a solid Shape is used in the FEM Workbench it will be discretized into a triangular mesh. In this case, the resulting object is a Fem FemMeshObject ( class), and is not derived from a Mesh Feature ( class).

For more information see FEM Workbench and FEM Mesh.