The primary communication channel between IT and the users is the Service Desk function. When a user contacts Service Desk, in principle the issue can concern anything at all. It might be a question, an order or someone who needs help with an IT service which is not working. That is to say, a request of some kind which has to be dealt with by Service Desk. The Request Fulfilment process exists in order to manage issues which arrive at Service Desk from users.
All issues from users start as service requests. The broad definition means that Request Fulfilment often consists of several procedures, depending on what is being requested.