The<unk>  (symbol:<unk>  is the International System of Units (SI) base unit of frequency. The definition of the<unk>  is based upon that for the second, namely: the hyperfine splitting in the ground state of the caesium 133 atom is exactly 9 192 631 770<unk> , 
ν
{\displaystyle \nu }
 (hfs Cs) = 9 192 631 770<unk> .
Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English,<unk>  is used as both singular and plural. As any SI unit,<unk>  can be prefixed; commonly used multiples are kHz (kilohertz, 103<unk> , MHz (megahertz, 106<unk> , GHz (gigahertz, 109<unk>  and THz (terahertz, 1012<unk> .
One<unk>  simply means one cycle per second (typically that which is being counted is a complete cycle); 100<unk>  means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1<unk> , or a human heart might be said to beat at 1.2<unk> . The frequencies of aperiodic events, such as radioactive decay, are expressed in becquerels.
To avoid confusion, periodically varying angles are typically not expressed in<unk> , but rather in an appropriate angular unit such as radians per second. A disc rotating at 60 revolutions per minute (RPM) can thus be said to be rotating at ≈6.283 rad/s or 1<unk> , where the latter reflects the number of complete revolutions per second. The conversion between a frequency f measured in<unk>  and an angular frequency ω measured in radians/s are:
Hertz
Germander
Enzyte
Amnion
Buchnera 
Kerion
Dermatophyte
Rouleaux