Raja yoga is the path of disciplined meditation, systematized in Patanjali‘s Yoga Sutras into eight limbs (ashtanga): ethical restraints (yamas), observances (niyamas), Asana (posture), Pranayama (breath regulation), pratyahara (withdrawal of the senses), dharana (concentration), dhyana (meditation), and Samadhi (absorption).
The path is progressive but not rigid. Later limbs depend on earlier ones but also deepen them; the whole structure is meant to be cultivated together over years.
Swami Vivekananda‘s Raja Yoga (1896) introduced this path to Western audiences and remains one of its clearest English expositions.