What is Classified Advertisement in SEO? The classified advertisement is an Off-Page SEO strategy which is used to post exciting deals and offers of a website into online classified submission platforms. Online classified ads can be categorized into two categories i.e. Free and Paid. Under free online classifieds advertisements, there is a limit of days for ads and in paid classifieds, the limit of days can get exceed with that too you can add more images, videos and other stuff.