In Hindu astrology, Mangal Dosha is an astrological combination that occurs if Mars(Mangal) is in the 1st, 2nd, 4th, 7th, 8th, or 12th house of the ascendant chart. A person born in the presence of this condition is termed a manglik.
It is believed to be unfavourable for marriages, causing discomfort and tension in relationship, leading to severe disharmony among the spouses and eventually to other bigger problems. This is believed to be caused due to the "fiery" nature of the planet Mars, named after the Roman god of war. Also, if two mangliks marry, the negative effects are believed to cancel each other out. However, Mars is not the only planet in Astrology that is supposed to affect the relationship and these effects should be seen in a broader perspective of overall astrological compatibility.
There is a belief that the negative consequences for a single-manglik marriage can be resolved if the manglik first performs a ceremony called a kumbh vivah, in which the manglik "marries" a banana tree, a peepal tree, or a silver or gold idol of the Hindu God Vishnu.
The bad effects of Mangal Dosh can be reduced with the help of astrological remedies which would generally include the application of Pooja, Mantras, Gemstones and Charities and these remedies are different for different individuals depending upon their horoscopes.