SW Maintenance: Change request

A CR is what has to be written (by us or sent by the customer) every time a system is under Change Management (e.g. after delivery) and you need to keep track of what needs to be altered. If it is under the project/maintenance contract scope it will not be charged to the customer. Otherwise, there'll have to be a new proposal (sometimes also called "change requests (proposals)" - with a price tag on it - that the customer shall approve formally before we proceed with any change whatsoever):

Change request - Wikipedia

An impact analysis could have to be done (in all aspects/deliverables of the system). The sum of the hours accounted in the PIA will be used to reach the final cost. This is why later a CR appears in the waterfall lifecycle the more expensive it will be (more artifacts - already approved or still being developed - will have to be reworked accordingly).

Quoting the several names that the CRs can have (other than CR and Software Change Request - SCR and Contractual Change Notice - CCN):

"Change requests have many different names, which essentially describe the same concept:

• Request For Change (RFC) by Rajlich (1999); RFC is also a common term in ITIL (Keller, 2005) and PRINCE2 (Onna & Koning, 2003).
• Engineering Change (EC) by Huang and Mak (1999);
• Engineering Change Request (ECR) at Aero (Helms, 2002);
• Engineering Change Order (ECO) by Loch and Terwiesch (1999) and Pikosz and Malmqvist (1998). Engineering Change Order is a separate step after ECR. After ECR is approved by Engineering Department then an ECO is made for making the change;
• Change Notice at Chemical (Helms, 2002); 
• Action Request (AR) at ABB Robotics AB (Kajko-Mattson, 1999);
• Change Request (CR) is, among others, used by Lam (1998), Mäkäräinen (2000), Dennis, et al. (2002), Crnkovic, Asklund and Persson-Dahlqvist (2003) and at ABB Automation Products AB (Kajko-Mattsson, 1999).
• Operational Change Request (OCR).
• Enterprise Change Request (ECR)."