It is one of the three domains that are part of a Business Domain. These subdomains are simple by nature and do not provide any competitive advantage to the business. Supporting domains usually resemble simple CRUD operations. They also do not change often and should not have a reason to do so, because they do not help the business to evolve. An example of a supporting domain could be a web application.
Implementation
These are implemented in house even thought they are not giving the business competitive advantage. It is mainly because those do not exist yet. Not too much attention should be given to those and you should not add unnecessary complexity to those. Also, those are usually implemented by low skilled developer, or they are outsourced.