Define Frequency : It is the number of times an event has occured per unit of time. Or in terms of waves frequency is described as the number of waves that pass a fixed point in a given duration of time. So if wave takes 1/10 second to pass, the frequency of wave is 10 per second.
SI unit of frequency is hertz. With Notation as Hz.
We have some handy frequency converters to perform frequency conversions.