Use the Base element to set the base URL that all document-relative paths in the page are considered relative to.
_blank loads the linked document in a new, unnamed browser window.
_parent loads the linked document into the parent frameset or window of the frame that contains the link. If the frame containing the link is not nested, then this is equivalent to _top; the linked document loads into the full browser window.
_self loads the linked document in the same frame or window as the link. This target is the default, so you usually don’t have to specify it.
_top loads the linked document in the full browser window, thereby removing all frames.