Cover art is a type of artwork presented as an illustration or photograph on the outside of a published product such as a book, magazine, newspaper (tabloid), comic book, video game, music album, CD, videotape, DVD, or podcast.
Harper's Magazine, June 1896, by Edward Penfield
Ivory book cover with scenes from the life of Christ, c. 800 AD
Uezdnoe, by Yevgeny Zamyatin, 1916
The Real Mother Goose, Blanche Fisher Wright, illustrator, 1916
A magazine is a periodical publication, generally published on a regular schedule, containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combination of the three.
German print magazines
Front cover of 1 October 1892 issue of The Illustrated London News
La Gazette, 26 December 1786
The Olympic Number of Life, 10 July 1924. Issues of general interest magazines focused on a specific subject were referred to as "numbers" and featured cover art relevant to the given topic, in this case the 1924 Summer Olympics.