What is a 'Guest'?

Can someone define a 'Guest' for me in Dolphin? Is it an unregistered visitor to the site? The reason I ask is many pages on my site by default allow a guest to view them, for example, Home pages of Groups, Articles, News, etc. These kind of pages I would only want visible by actual logged in Members. Do I just uncheck 'Guest' to ensure that? It seems logical to me but I don't like to go through every page presuming & it doesn't work. Thanks guys.

Edited to add: I should have stated the Blocks on these pages are visible to 'Guests'. Which leads me to ask, if I uncheck them all would an unregistered visitor just see a blank page on those that I don't want them to see? Thanks again.

A guest is a person who is not logged in to the site. Yes, you would uncheck the Guest box for any blocks that you only want viewable to logged in persons.

Thanks for your quick response. It seemed pretty logical I know but there are some blocks visible I would have expected to be invisible to Guests by default. Thanks again.