“An organizational body or entity assigned various responsibilities related to the centralized and coordinated management of those projects under its domain. The responsibilities of the PMO can range from providing project management support functions to actually being responsible for the direct management of a project”
“PMO is the administrative mechanism by which a focal point is provided for organizational project management activities”
“A project management office is a formal, centralized layer of control between senior management and project management”
Refer to the page on “PMO Functions” to see what responsibilities are typical of PMOs (e.g. Templates, Methodology, etc)
Other popular names for the same type of entity are: Program Management Office, Project Support Office, Project Office, Center of Excellence, etc.
The letter “P” in PMO stands for “Project” (and not Program or Portfolio). PMO also refers to a multi project office, that is, one PMO to oversee all projects in an organization rather than one PMO for each project. Those projects may be independent of each other, or they may be related and contributing together towards the same outcome as a single Program, or may be grouped in a Portfolio to facilitate their effective management towards meeting a strategic business objective.
This definition is aligned with the PMI terminology used in PMBoK and to the PMO whitepaper by Hobbs
 PMI. (2003) Guide to Project Management Body of Knowledge (2003) PMI [online with subscription] (URL http://www.pmi.org)
 Parviz, F. (2001) Is Your Organization a Candidate for Project Management Office (PMO)? AACE International Transactions, 2001, p7.1, 4p
 Martin, N. L.; Pearson, J. M; Furumo, K. (2007) IS Project Management: Size, practices and the project management office. Journal of Computer Information Systems, Vol. 47 Issue 4, p52-60
 Hobbs, B. (2007). The Multi-Project PMO: A Global Analysis of the Current State of Practice. A White Paper Prepared for Project Management Institute. PMI. [online with subscription] (URL http://www.pmi.org)