The number of rotations divided by time: \[f_{\text{rot}}=\frac{\text{d}N}{\text{d}t}\] The synonyms rate of rotation, rate of revolution, centrifugal speed, centrifugation speed, and the traditional units of rotational frequency such as revolutions per minute, r.p.m., ppm, rev. min-1, r min-1, are not recommended.
Sources:
PAC, 1994, 66, 897. 'Quantities and units for centrifugation in the clinical laboratory (IUPAC Recommendations 1994)' on page 904 (https://doi.org/10.1351/pac199466040897)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 991 (https://doi.org/10.1351/pac199668040957)