The short answer is that it is a RhinoCommon object!
Under the hood, your mesh object is an openNURBS mesh. You can use the rhino3dm python library to write this mesh to .3dm file, and then open it in Rhino, or serialise it to JSON and send it to a web server.
# sample: create model, add mesh and write to .3dm file
model = rhino3dm.File3dm()
What is it that you want to do with this mesh object? Knowing a bit more about how you want to use rhino3dm will help us to provide some more relevant information.