Standing wave velocity

The velocity term here means the speed of a wave traveling through the medium. Take, for instance, a pipe resonating, like in an organ (the equations are basically the same). The v term means the speed of sound in air, even though the wave is standing. The same thing applies here - v means "speed of any wave" not just "speed of this particular wave".

The velocity of the standing wave is the velocity of the incoming and reflecting wave that formed this standing wave. See http://www.physicsclassroom.com/class/waves/Lesson-4/Formation-of-Standing-Waves