Vmu - Minimum Unstick Velocity
I have no connection to Gulfstream and thus my comments are not specific to this event.
Vmu is the minimum unstick speed. It is the minimum speed at which the airplane can generate enough lift with its tail on the ground to takeoff. This speed ends up being the basis for some of the takeoff operational speeds and associated field length requirements.
The testing to demonstrate / determine Vmu involves rotating early and having the tail in contact with the ground at the time that liftoff occurs. The trick is to get the tail down at just the right moment so that it does not drag too much and yet the demonstrated Vmu is as low as possible. Tail skids (a suitable block of wood) are often used during this testing.
I am aware of control law provisions on non-Gulfstream fly-by-wire airplanes that reduce the likelihood of an inadvertent tailstrike during takoff, but I don't know of any that completely prevent hitting the tail. To do so would be to reduce the available performance of the airplane and thus in my opinion would not be wise.