This flag is used to mark pages that should be deleted. Sometimes this is because the page is spam or not about topics applicable to the site. Note that pages that should be merged with others do not get this flag.
Manual of Style
If an article has this flag, the community should decide if it does indeed meet the criteria for deletion and then an administrator should delete it.
If the page is not clearly spam and there's a primary author of the page (for example, it was created recently by someone) at least some effort should be made to involve that person in the deletion discussion before deleting. Failing that, at least getting a quick sanity check "SGTM" from someone on IRC is reasonable before deleting. If the discussion gets more involved, it should move to e-mail.
If you check off this flag you should include a Template:Editorial/Deletion_Candidate template to specify details about why it's being considered for deletion.