A partwork is a written publication released as a series of planned magazine

Magazine

Magazines, periodicals, glossies or serials are publications, generally published on a regular schedule, containing a variety of articles. They are generally financed by advertising, by a purchase price, by pre-paid magazine subscriptions, or all three...

-like issues over a period of time. Issues are typically released on a weekly, fortnightly or monthly basis, and often a completed set is designed to form a reference work on a particular topic.
Partwork series run for a determined length and have a finite life. Generally, partworks cover specific areas of interest, such as sports, hobbies, or children's interest and stories such as PC Ace

PC Ace

PC Ace was a partwork magazine published by Eaglemoss Publications, between 1999 and 2001. It was aimed at those aged between 10 and 14, providing information on how to operate a personal computer...

and the successful The Ancestral Trail

The Ancestral Trail

The Ancestral Trail is a now out-of-print partwork magazine that was originally published by Marshall Cavendish in the United Kingdom, Australia, South Africa and New Zealand in the early nineties. It was also translated into French, German, Italian, and Spanish and licensed for sale worldwide...

series by Marshall Cavendish

Marshall Cavendish

Marshall Cavendish is a subsidiary company of Times Publishing Group, the printing and publishing subsidiary of Singapore-based conglomerate Fraser and Neave and at present is a publisher of books, directories and magazines. Marshall Cavendish was established in the United Kingdom in 1968 by Norman...

 Ltd.