Advertorial content is a cross between free editorial and a straight paid-for advert. It is paid for by the advertiser, to appear in a media outlet, traditionally a glossy magazine, but also these days in digital publications.
Also known as native advertising, it is usually written in the same journalistic style as the publication in which it appears. This requires someone who is experienced in writing in a journalistic style and is also able to match the style of the outlet in which the advertorial is published.
Since it is paid for, the content of the advertorial is controlled by the advertiser, but it must meet the in-house style of the publisher. Is in distinct in tone and language from a marketing approach, which would appear in a traditional style advert or brochure. The advertorial is usually best accompanied by good quality photographs to support the article.