Most of the models that Westhinghouse made began with "OV". What does it mean?

probably nothing but the model number.

Correction: Most of the roadway models begin with OV.  OV stands for "Oval"  It's a carryover from the clamshell era when you had the OV-20, Revere's "Endoval", and Line Material's "Ovalite".

so what does the ov stand for in cooper/crouse-hinds models.because the ovl,ovx,ovf,ovd were designed to replace the older ov series

Still means the same thing.

Line Materials were made by McGraw Edison. McGraw Edison later on made their own model streetlights. Westinghouse & Line Materials & McGraw-Edison were later taken over by Crouse-Hinds. Cooper Lighting later toook over the Crouse-Hinds lighting department. I guess means in the streetlighting family tree you would see EATON being the top of the family tree as Eaton has Cooper & Crouse-Hinds as their brand of lighting managed by Cooper lighting.