The Civil Airband in the UK (118-137) has a spacing of 8.33 Khz, ATC may refer to either the actual transmit-receive frequency such as 124.000 or it’s channel reference which would be 124.005, the channel is for radio’s fitted to aircraft and airport installations, in general terms outside of this it is always the frequency that is required you can use the database search below to find a frequency vs channel allocation