In communities of artists and art fans, a request is a request for the creation of an artwork (such as a drawing). A request can either be directed at a specific artist, or at anyone who happens to read it. A request will typically describe a scene or subject matter that the person would like to see, such as specific characters and what they could be doing in the picture.
A request is different from a commission in that a commissioned work is paid for. A person who commissions an artist expects them to create the work within an agreed time and quality. In return for payment the commissioner also often gets the original work, and/or exclusive or non-exclusive usage rights.
A request, on the other hand, is made with no expectations or payments of any kind, but instead ask them for free, hoping that an artist will pick up their suggestion and share the finished work because they feel inspired to do it.
Unsolicited requests are not always welcome because they can become an annoyance for artists, and a spam problem in forums. Some spanking art forums, such as Anime OTK, have policies that strictly forbid the posting of requests anywhere on the site for certain reasons.