Commonly called the turnover number, N, and defined, as in enzyme catalysis, as molecules reacting per active site in unit time.
PAC, 1976, 46, 71. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis' on page 81 (https://doi.org/10.1351/pac197646010071)