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The tidal range is the vertical difference between the high tide and the succeeding low tide. Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.
Different parts of the world experience different tidal regimes. Around the UK, there are mostly two high tides and two low tides each day: this is called a semi-diurnal regime. Other parts of the world have a diurnal tidal regime with only one high tide and one low tide each day. The difference in height between high tide and low tide is called the tidal range.