What is the meaning of the curvy line in $\widetilde{\sin}\theta$ and $\widetilde{\cos}\theta$?

Question

I am Electrical Engineer, and iI am facing problems with solving inner space vectors. I am trying to understand it, but i can't completely understand what this curvy line represents and how it differentiates a simple sine wave from the one with a curvy line on top of it.

Here are the symbols in context: