What is "drive voltage" for a MOSFET?
Real MOSFETs are not perfect devices, they don't simply turn on or off with applied Gate-Source voltage. The amount of "ON" current through Source to Drain is a function of applied GS voltage. It is a steep function, but still a continuous one. This is an example of this dependence, from a tutorial:


Datasheets for MOSFETs are trying to simplify this functional parameter by supplying "corner" points. 

The V"th" voltage is the voltage where the drain current is barely measurable, in the OP case it is 250 uA, which happens at 4 V.

The "drive voltage" (listed as 10V) is the voltage when the MOSFET is conducting to full specifications, and can deliver 8.4 A of current and having the specified Rds(on) resistance of less than 0.2 Ohms.