The truth or falsehood of all man's conclusions, inferences, thought and knowledge rests on the truth or falsehood of his definitions." -Ayn RandAyn Rand taught the importance of knowing exact definitions. In the course of her re-conceptualization of key philosophic issues, she formulated brilliant new definitions of many concepts. Building on her base, Leonard Peikoff has nearly doubled the number of philosophic terms formally defined by Objectivists.This glossary was originally conceived as a compilation of these formal definitions. After reviewing the literature, however, we decided to broaden its scope to include terms that meet at least two of the following three criteria: (1) the term has a formal definition (or near to it), (2) it is philosophically important, (3) its meaning is dramatically clarified by Objectivism.Thus, in addition to formal definitions, this glossary includes characterizations that are near-definitions of terms (though not meeting the requirements of formal definitions), statements of philosophic principles, and descriptions of axiomatic concepts. (Since axiomatic concepts can be defined only ostensively, the entries for these terms are merely descriptions.)