If there is present a relationship (combination, bidirectional vision or exchange of zodiacs) between two or more than two planets (out of which atleast one should be the lord of 'Kendra' & the other should be the lord of 'Trikon') in a birth chart than these planets are said to be constititing a 'Rajyog' in Kundli or birth chart. This 'Raja Yoga' in Vedic Astrology is said to give benefits to the person concerned related to the houses in which this 'Raj yog' has taken place or related to the houses of which the planets constituting 'Rajyog' are having a lordship. Rajyog in Kundli doesn't necessarily mean becoming a king. Usually its benefits are observed in a person's life when there is mahadasha of one planet and the antardasha of another planet in the person's life, provided both planets are constituting Rajyog in some way in the person's birth chart.

Examples of Rajyog -

Example#1: - In the chart given below there is a combination relation between Mars & Jupiter in the 4th house which is constituting a Rajyog. Mars is the lord planet of 4th as well as 9th house (4th house is Kendra) whereas Jupiter is the lord planet of 5th as well as 8th house (5th house is Trikon). Mars is itself constituting a Rajyog (without the aid of any other planet) because it is the lord planet of Kendra as well as Trikon. This way there are two Rajyogs in this chart.

Example#2: - In the chart given below Mars is present in the 4th house & Jupiter is present in the 10th house of the chart & both planets are watching each other with their 7th visions. So there is a bidirectional vision relation which is constituting a Raja Yoga because Mars is the lord planet of both a Kendra & Trikon and Jupiter is the lord of Trikon.

Example#3: - In the chart given below Mars is present in the 5th house on the sign of Sagittarius (which is the sign of Jupiter) & Jupiter is present in the 4th house on the sign of Scorpio (which is the sign of Mars). This way both Jupiter & Mars have exchanges houses or zodiacs & this exchange is constituing a Rajyog because Mars is the lord planet of both a Kendra & Trikon and Jupiter is the lord of Trikon. .

Google