You're using terms in the wrong way.
Responsive can apply to any style that responds based on the size of the window it is being rendered in. (There's more to it than that, but that's the basic premise).
When a style is responsive, some of the "responses" it can have to things like a window being resized, or loading on a smaller screen would be to hide elements, make elements smaller, make elements bigger. Change the width of elements so they are percentage based rather than fixed etc.
So effectively a responsive design can alter a fixed width style to be fluid -- and vice versa, I guess.