Co-citation constitutes an SEO concept whereby two websites get mentioned together on some third-party site without a direct link joining them. This association also assists search engines in understanding the relationship between those sites and how that contributes towards website relevance, in addition to authority on particular subjects. For example, Website A and Website B may be mentioned frequently together in industry-related articles, which could automatically be perceived by search engines to be thematically related. More of a subtle contributor to link-building strategies, it also comes into play in enhancing brand visibility or boosting search engine optimisation from contextual relevance.