Virtual Condition Boundary Theory - A theoretical boundary limits the location of the surfaces of a feature of size.
Worst-case Boundary (WCB) - A general term to refer to the extreme boundary of a feature of size that is the worst-case for assembly. Depending upon the part dimensioning, a worst-case boundary can be a virtual condition, inner boundary, or outer boundary.
Zero Tolerance at MMC - A method of tolerancing part features that includes the tolerance geometric value with the feature of size tolerance and states a zero at MMC in the feature control frame.