Answer 1

Is variation caused by the process. It is produced by the interaction of aspects of the process that affect every occurrence

Answer 2

Those sources of variation in a process that are truly random, inherent to the process itself.

Answer 3

Causes of variation that cause the "natural variation" of the process. The result of the accumulation of the many tiny things that are continually varying each time the process is run. Such a process is "in control" or "stable" as seen on a control chart. Contrast special cause variation and Out of Control.