Vakri grahas are those planets of the Solar System other than Sun and Moon that appear to move backwards apparently due to earth’s orbit. Vakri in Sanskrit means twisted or crooked, indirect, evasive and ambiguous.
Vakragati means retrograde motion. As the Earth passes by a planet the planet seems to move backwards amid the stars. This phenomenon is known as retrograde motion. Retrograde motion of a planet is an illusion, the planet only appears to retrograde, actually it does not.
The Sun and the Moon do not have Vakra state and they do not acquire retrograde motion. Other five grahas have Vakra state and they acquire retrograde motion whenever they transit from fifth to eighth house from the Sun. Rahu and Ketu have perpetual retrograde motion. When planets are free from vakragati they are known as Margi grahas that are believed to be moving towards light.
A planet lying between two Vakri grahas behaves as a Vakri graha. Mangal, Brihaspati and Shani are retrograde in the signs opposite to the one occupied by the Sun. Buddha and Shukra appear to retrograde when they are farthest away from the Sun. Mangal gives the results of the third house, Buddha gives the results of the fourth, Brihaspati of the fifth, Shukra of the seventh and Shani of the eighth house from the house of its occupation. Vakri graha does not produce results uniformly. Vakri Grahas owning good houses produce good results and if owning bad houses produce bad results.
Vakragati in general intensifies the effects of planets for good or evil according to their functional attributes and position at the time of birth. They can confer both Raja yoga during its Dasha or throw one out of power or inflict adverse effect.