A render box?? Where did it go?

in New Users
I clicked on something and it put up a 'box" around what I was going to render. I could change the size and then fit my image inside. I have no idea what I clicked but I sure would like to find it again. Would anyone know what I'm talking about?
Comments
I found it. Show Aspect Frame.
I knew what you were talking about.
awesome! prixat. I found it by accident and forgot to write down where and what I found. I don't know of any other way to really tell if my images are coming out the right size.