Episteme
"Episteme" is a philosophical term derived from the Ancient Greek word ἐπιστήμη "epistēmē", which can refer to knowledge, science or understanding, and which comes from the verb , meaning "to know, to understand, or to be acquainted with".
Epistemocracy
However the term had already been used long before this, and Taleb's usage has not caught on. Most uses of the word are unrelated or even opposite to this. For instance in reference to communism: "Maoism, like the Marxist- Leninist system upon which it modeled itself, was an `epistemocracy,' rule by those possessed of that infallible wisdom embodied in the `universal truth of Marxism'" Or theocracy: "The model for this concentration of knowledge in the hands of a single group is the epistemocracy of the Old Testament priests..."