That is not a standard notation, so what follows is only a guess. I suspect that the V stands for variation. So the question is possibly asking for the total variation of the function over the given interval.

For example, the function increases from –1 to 1/2, and then decreases from 1/2 to 2. So its total variation over the interval [–1,2] is the amount that it increases between x=–1 and x=1/2, plus the amount that it decreases between x=1/2 and x=2.