They are typically used in Webmail and more generally for page navigation. They allow independent scrolling of separate documents - you can have one frame with a list of links, and the other frame to load the pages in.
Location is specified using the src attribute.
This cannot be less than 1. Long descriptions should describe the frame, not its content. Thus by addition of the target attribute, the page is set to load in a different frame. This content will only be rendered if frames are unsupported. See copyright document for terms of use.