Ancient Yoga philosophy prescribes four spiritual paths to attain knowledge of the Self: karma-yoga, the path of selfless action; bhakti-yoga, the path of devotion; raja-yoga, the path of concentration and meditation; and jnana-yoga, the path of knowledge and discrimination.
Swami Vivekananda has expounded these beautifully in his famous lectures given to the Parliament of Religions and other places in 1893 and later. All his writings are available online. A must read for those who wish to know.
Raaj Yoga alsa refers to the state in which a person is a Raja and yet a Yogi (a sansari as well as a sadhu).
In Gurmat Raj Yoga means path of Naam AND Keertan which makes the gurmukh a 'Raja Sagli Srisht Ka'.
'Raaj Leela Terai Naam Banaee, Jog Banya Tera Keertan Gaee'
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥