firstly coax is not coax - there are many grades - more about the insulation than the copper wire running through it
actually coax IS coax. i did specify that grades vary though. a coax cable is still coax cable regardless if it is high or low grade cable.
Coaxial simply means one conductor inside another. There are.hundreds of coax types with different characteristic impedance, constructed with different dielectric, inner and outer conductor materials and diameters etc etc.
In the narrow context of VM cabling, only a very limited number of coax types are suitable. Most cables used for standard TV aerial downloads would not be suitable and I would hope the VM installer should know this