The FAA defines V-1 as the speed the maximum speed at which the takeoff maneuver can be initiated and the airplane stopped within the remaining field length under the conditions and procedures defined in the FAR's. Also the "go procedures, but this does not apply this particular discussion.
It has changed from a decision speed to an action speed. My airline teaches the V-1 call at V-1 minus 3 knots in order to initiate an abort by V-1.You can go to Faa.gov and search "takeoff safety" or go/no go decision. Way too much to post here, but full of good info.