These are attributes of Anchor Tags

target="_self" ~ Your site will open in the same window you are working on.(This is default value) / Your site will open in the current frame.

target="_blank" ~ Your site will open in the another window you are working on.

target="_parent" ~ Your site will open in the parent frame of the current frame.

target="_top" ~ Your site will open in the topmost frame in the nested frames.

Today, iframes are not used. iframe was a tag which was a collection of many frames. It was a concept of nested frames.