The wavelength of a wave is the distance from a point on one wave to the same point on the next wave. For example, it is the distance from one crest to the next crest, or from one trough to the next trough. Wavelength is measured in metres (m).
The frequency of a wave is the number of waves passing a point each second. It is also the number of waves a source produces each second. It is measured in hertz (Hz), where 1 Hz means one wave per second. A source that produces 50 waves every second has a frequency of 50 Hz.
Large frequencies use prefixes. 1 kHz is 1000 Hz, so 2 kHz is 2000 Hz. A radio wave might have a frequency of several MHz, where 1 MHz is 1 000 000 Hz.
