Self-publishing is the publication of media (e.g. books, music, art) by its author at their own cost, without the involvement of a publisher.
However, the author may engage professionals or companies to assist with various aspects of publication, distribution or marketing.
This page lists the best-known of such companies.
Assisted self-publishing companies offer services such as editing, proof-reading, cover design, formatting, printing, marketing and promotion.
They also provide higher royalties as compared to traditional publishing houses.