The number of waveperiods per time interval. The linear frequency, , is the number of cycles per time interval. SI unit .
For the angular frequency the symbol () is used with as the SI unit.
See also: a more general definition of frequency
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 345