There is only one file type that uses the .LWO extension:
LightWave 3D Object File
Three-dimensional object created by LightWave 3D, a program used for 3D modeling, animation, and rendering; contains points, polygons, and surfaces that describe the object's shape and appearance; may also contain references to image files used for object textures.
LWO files are saved in the LWO2 format beginning with LightWave 6.0. They may also be exported by Foundry Modo, which is another 3D modeling program.
Updated: October 31, 2017