Saharan dust is a mixture of sand and dust from the Sahara, the vast desert area that covers most of North Africa.
As in other parts of the world, the wind can blow strongly over deserts - whipping up dust and sand high into the sky. The wind in the upper part of the atmosphere then transports the dust in the direction in which it's travelling, sometimes towards the UK.
Once it is lifted from the ground by strong winds, clouds of dust can reach very high altitudes and be transported worldwide, covering thousands of miles.
In order for the dust to get from up in the sky down to the ground, you need something to wash it out of the sky - rain.
When the raindrops fall, they collect particles of dust on the way down. Then when the raindrops land on something and eventually evaporate, they leave behind a layer of dust.
Paul Hutcheon, Met Office forecaster, says: "We usually see this happen several times a year when big dust storms in the Sahara coincide with southerly winds to bring dust here."
In certain weather situations, Saharan dust can also affect air quality and pollution levels.
A recent example of Saharan dust was in March 2014 when people across the country set off to work on a Monday morning, puzzled after finding their vehicles coated with a thin layer of red dust.
The satellite animation in this video shows the air flowing from North Africa over Europe and the UK, with gale force wind conditions in the Sahara of over 4o miles per hour bringing a steady flow of dust over several days.
For more information take a look at the Met Office blog.
Last updated: 23 December 2015