Implied Datum - An assumed plane, a

Implied Datum - An assumed plane, axis, or point from which a dimensional measurement is made.
Inclined Datum Feature - A datum feature that is at an angle other than 90o, relative to the other datum features.
Inner Boundary (IB) - A worst-case boundary generated by the smallest feature of size minus the stated geometric tolerance (and any additional tolerance, if applicable).
International Standards Organization (ISO) - The organization that published an associated series of standards on dimensioning and tolerancing.