Commercial Drawings is a tag used to indicate works that are created for commercial use.
Overview
This tag is only usable only if you receive a work request from companies. These works may be used for, but not limited to : Light novels, game characters, settings, art exhibition, promotion and many more. Usually these works are mainly for commercial, used by the artist to promote their own product. However, this tag can also used for doujin products as well.
One thing to note is that these artist do not draw this for the fun of it, but actually drawn by request from the company that commissioned them. When such artwork is posted in pixiv, it means the company and the artist have both reached an agreement beforehand.
Without the permission from the artist AND the company beforehand, one should NEVER use the artwork for other purposes (such as reposting it on other websites), as the artwork belongs to both the artist, and the company. Hence both sides have the right for it.
Regardless of purpose, it is considered a breach of rules the moment you use the artwork without permission, so be sure to confirm things beforehand.