A mesh is a collection of triangles that are connected by common vertices. If every edge of every triangle in the mesh is connected to another triangle in the mesh (there are no gaps or holes in the mesh) the mesh is called an "enclosed mesh".
Meshes are not first-class objects to Misfit Model 3D, but there are some operations where use of the term mesh can be helpful.
Note that the term "mesh" is distinct from "group". The term "group" in MM3D generally refers to a collection of triangles that have been defined as a group and may have a material applied. Triangles in a mesh may or may not be in a group.
Creating a Mesh
Meshes are created when you use the creation tools to create geometric shapes such as cubes, spheres, or cylinders.
Other Mesh Details
You can combine meshes using the Boolean Operataions panel. For the union, intersection, and subtraction operations to work properly, all meshes involved must be enclosed (otherwise the behavior of the face-removal step is undefined). If the meshes are not enclosed you can still use the fuse operation and manually remove the faces that must be removed.
The Simplify Mesh command is useful for combining faces that do not add detail to a shape. For example if you have a cube where each side is made up of 8 triangles, then all of these triangles are in the same plane and many edges form a single straight line. In this case, the eight faces on each side can be reduced to two faces. Often when you use a boolean operation to combine two objects you will want to use the simplify mesh command to eliminate unecessary faces from the model.
If you have mesh that is not enclosed you can use the Cap Holes command to create faces to fill in the gaps. Note that the cap holes feature is very limited. If your shape is relatively complex it may have difficulty correctly determining how to connect faces to fill in the gaps.