Scope creep (also called requirement creep and feature creep) in project management refers to uncontrolled changes or continuous growth in a project’s scope. This can occur when the scope of a project is not properly defined, documented, or controlled. It is generally considered harmful.
If budget, resources, and schedule are increased along with the scope, the change is usually considered an acceptable addition to the project, and the term “scope creep” is not used.
Scope creep can be a result of:
- poor change control
- lack of proper initial identification of what is required to bring about the project objectives
- weak project manager or executive sponsor
- poor communication between parties
- lack of initial product versatility
Scope creep is a risk in most projects. Most megaprojects fall victim to scope creep (see Megaprojects and Risk). Scope creep often results in cost overrun. A value for free strategy is difficult to counteract and remains a difficult challenge for even the most experienced project managers.
A simple tool to measure scope definition is available. The Project Definition Rating Index (PDRI) was developed by the Construction Industry Institute for industrial projects (1996) and for building projects (1998). A version has also been developed for IT projects. Studies show that projects with a score less than 200 had smaller cost overruns, were on schedule rather than behind schedule, and had substantially fewer change orders when compared with projects having PDRI scores over 200. 
- What is PDRI (Feb 2014) 
- A Comprehensive Series on Scope Creep
- The Creeping Scope - How Accurate can Project Documentation be?
- Wideman Comparative Glossary of Project Management Terms by R. Max Wideman P.Eng. FCSCE, FEIC, FICE, Fellow PMI