Retrograde motion of a planet is its apparent backward motion through the sky, as observed from Earth. This apparent retrograde motion is caused by the Earth traveling past a slower-moving outer planet (Jupiter, Saturn, Uranus, Neptune and also Pluto, even if from 2006 Pluto is considered only a dwarf planet) or when the Earth is itself passed by a faster-moving inner planet (Mercury, Venus or Mars).
So, this is like the apparent motion of the slower car on the highway – an optical illusion. But it is important, from our perspective: we live on Earth and we judge things from an earthly perspective.
Some astrologers consider this apparent backward movement of the planets was to be unlucky, because it goes against the natural order of movement – the direct movement. But a retrograde planet is not necessarily something bad – actually, it is a chance to recognize, understand and correct past mistakes.
Mercury retrograde in Aries: March 22nd-April 15th
Mercury retrograde in Leo: July 26th-August 19th
Mercury retrograde in Sagittarius and Scorpio: November 16th-December 6th
Venus retrograde in Scorpio and Libra: October 6th-November 16th
Mars retrograde in Aquarius and Capricorn: June 26th-August 27th
Jupiter retrograde in Scorpio: March 8th-July 10th More about Jupiter retrograde in Scorpio
Saturn retrograde in Capricorn: April 17th-September 6th
Uranus retrograde in Aries: August 2nd, 2017 – January, 2nd, 2018
Uranus retrograde in Taurus and Aries: August 7th, 2018-January, 6th, 2019
Neptune retrograde in Pisces: June 18th-November 24th More about Neptune Retrograde
Pluto retrograde in Capricorn: April 22nd-September 30th