Variation is a common concept in project management. It is considered as one of the major uncertainties project managers need to monitor as well as deal with all the time.  It is defined as the actual condition that is entirely different from the expected condition. The expected condition is usually contained within a baseline plan.

Variations can exist within the project in costs, activity durations, performance level and amount of resources available. Although different types of variations exist, the project plan still remains intact but the variation of the schedule or project can somehow affect the delivery of the project team.

In the context of project management,  a lot of variations exists particularly in the quality of the project or deliverables that can affect customer satisfaction. This is the reason why variation needs to be measured. In project management, the Quality Metrics measure the allowable variations of the product, service and result. There are many statistical methods that are available to monitor the variations that exist within a particular project. Examples include control charts, sensitivity analysis, and many other analytical techniques.

This term is defined in the 5th edition of the PMBOK.