A350: VMU tail strike test will be one of the first to be done next summer

This test allows to determine speeds which are called VMU (Velocity Minimum Unstick). Airbus needs to know the VMU because the computed take off speeds incorporate some margin above VMU, just as they also do for VS (Stall speed), VMCG (Minimum control speed on the ground) and VMCA (Minimum control speed in the air). These "V" speeds therefore form the basic building blocks of take-off performance.

http://bloga350.blogspot.com.es/2012/12/vmu-tail-strike-test-will-be-one-of.html