The inherent range of variation in a process, as determined by process performance measures.
Natural bounds are sometimes referred to as “voice of the process.”
Techniques such as control charts, confidence intervals, and prediction intervals are used to determine whether the variation is due to common causes (i.e., the process is predictable or stable) or is due to some special cause that can and should be identified and removed. (See also “measure” and “process performance.”)

National Defense Industrial Association

An item that was developed prior to its current use in an acquisition or development process.
Such an item can require minor modifications to meet the requirements of its current intended use.

Requirements affecting product and service acquisition or development that are not properties of the product or service.
Examples include numbers of products or services to be delivered, data rights for delivered COTS and nondevelopmental items, delivery dates, and milestones with exit criteria. Other nontechnical requirements include work constraints associated with training, site provisions, and deployment schedules.