The noun baseline in general usage refers typically to the conditions that exist at a given point, usually the start point, of an activity, study, or project. An example of this usage can be found in medical studies, in which participants vital signs and other measurements at the start of a study are referred to as their “baseline measurements”.
In the field of project management, baseline represents the approved time phase plan for a particular item or a project phase, factoring in the addition or subtraction of approved project cost, scope, schedule, and technical changes. This approved time phase plan can apply to a number of components of a project, including the project as a whole, a work package, a schedule activity, or a work breakdown structure component. The term baseline, although in most common usage applies to the current baseline, can be used to refer to the original baseline (or some other specific baseline altogether). The term baseline in project management is typically used with a modifier of some sorts. Some examples of this are “cost baseline“, “performance measurement baseline”, and “technical baseline”. For more information, see performance measurement baseline.