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The 'prevailing winds' are the trends in speed and direction of wind over a particular point on the earth's surface. A region's prevailing winds often reflect global patterns of movement in the earth's atmosphere.

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Geostrophic winds

References

Geostrophic winds

The prevailing surface winds are calm at the equator (the doldrums), then they blow from the northeast immediately north of the equator and from the southeast immediately south of the equator: these are called the trade winds because they allowed early European ships to sail from east to west to the Americas. Around 25 degrees north and south, near the tropics, the winds calm again in the horse latitudes.
Most of this activity is due to air pressure. At the equator, the heat causes air to rise, creating a belt of low pressure in the doldrums. After the air rises, it flows north and south high in the atmosphere until it cools enough to subside, creating belts of high pressure in the horse latitudes. All of that extra air has to go somewhere, so it blows towards the equator as the trade winds, and towards the middle latitudes as the prevailing westerlies.
Meanwhile, at the poles, the cold causes air to subside, increasing the air pressure to cause the polar highs. As with the horse latitudes, the extra air has to flow somewhere, so it flows back in the direction of the equator as the polar easterlies, creating the far northern and southern climates of the world.

References

★ Prevailing winds at Manchester Municipal University

★ Prevailing winds and general circulation patterns at InfoPlease encyclopedia