100 percent flower frog for the bottom of a vase to help the flowers stay in their arrangement. Search 'glass flower frog' - images on any search engine ... thousands of them out there.
It's definitely not a flower frog, though I can see why it looks like one. Those bumps are convex, not concave. There's no way for a flower to be attached to this piece. I think it's a whiskey glass or something similar.