VHF is a short way of naming one group of radio waves. It comes from the first letters of Very High Frequency. Frequency means how fast the wave shakes each second, so VHF waves shake quite fast — faster than the AM radio band, but slower than the ones your phone uses. What matters to a learner is what this group of waves is good for. VHF gives clear, clean sound with little hiss, so it is what FM music radio and old broadcast television used. It is also what ships, small planes, air traffic control, police and mountain rescue teams talk on, because the sound is easy to understand. Its weak point is distance: VHF waves travel mostly in a straight line, so hills and buildings block them, and they do not bend far round the earth. That is why FM radio fades when you drive into a tunnel or over a mountain, while AM keeps going. You say the three letters one by one, V-H-F. It is used as a noun ("We heard them on VHF") and very often before another noun (a VHF radio, the VHF band, a VHF antenna). It is a fairly technical word — you meet it in boats, aircraft, walkie-talkies and radio equipment, not in ordinary conversation. Note that the dictionary line "waves that move very quickly" is about the shaking of the wave, not about speed of travel; all radio waves travel at the speed of light.