https://doi.org/10.1351/goldbook.P04493
Time for one cycle of a periodic phenomenon.
Sources:
Green Book, 2nd ed., p. 11 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 986 [Terms] [Paper]