Menu: Files->Export->Meshio
With this option it is possible to write a lot of mesh formats, through the use of the 'meshio' Python library (https://github.com/nschloe/meshio)
Note: most of these formats can be written with other alternative GiD commands, and usually with better features (faster and exporting more data, not only the mesh).
There are various mesh formats available for representing unstructured meshes. meshio can read and write all of the following and smoothly converts between them
Abaqus (.inp), ANSYS msh (.msh), AVS-UCD (.avs), CGNS (.cgns), DOLFIN XML (.xml), Exodus (.e, .exo), FLAC3D (.f3grid), H5M (.h5m), Kratos/MDPA (.mdpa), Medit (.mesh, .meshb), MED/Salome (.med), Nastran (bulk data, .bdf, .fem, .nas), Netgen (.vol, .vol.gz), Neuroglancer precomputed format, Gmsh (format versions 2.2, 4.0, and 4.1, .msh), OBJ (.obj), OFF (.off), PERMAS (.post, .post.gz, .dato, .dato.gz), PLY (.ply), STL (.stl), Tecplot .dat, TetGen .node/.ele, SVG (2D output only) (.svg), SU2 (.su2), UGRID (.ugrid), VTK (.vtk), VTU (.vtu), WKT (TIN) (.wkt), XDMF (.xdmf, .xmf).