This setting allows you to set up specific keywords that can be linked to specific pages - either it being internal or external pages. If a Keyword Search bar is set up on your website, users can type in a keyword in it and will take them to a page or website the keyword was linked to.
Internal Keywords: Keywords that can be linked to internal pages - or pages from your website.
External Keywords: Keywords that can be linked to external pages or websites.
You can set up multiple keywords to link to one page. To achieve this, in the Keywords field you would type them in like this: Keyword #1, Keyword #2, Keyword #3, ...
The Keyword Search bar is not case-sensitive, so users can type the keywords out without using capital letters.