Consider the classical wave equation. http://www.google.com/imgres?q=clas...w=196&start=0&ndsp=19&ved=1t:429,r:0,s:0,i:73 Does the v in the equation stand for the wave speed or the wave velocity? The image says v is the wave velocity but I am not sure about that as other sources like Wikipedia say that v is the wave speed. So, what is v really - speed or velocity? I think it's wave velocity since v is squared, so that allows for the possibility for v being positive or negative. And the direction of travel is the direction of the wavevector. What do you think?