Those figures represent the 'frame rate', in Hz. (i.e. they indicate the number of frames per second that are used to produce an image).
As television was developed across the world, manufacturers were forced (by the constraints of technology at the time) to set the scan rate, for the electron beam inside a cathode ray tube, to match the frequency of the local electricity supply. The USA's electrical system has an AC current with a frequency of 60Hz. So NTSC TV signals use a 60Hz standard. In Europe, mains electricity is supplied at 50Hz, so PAL and SECAM TV signals use a 50Hz standard.
Chris