Rāja Yoga (”royal yoga”, “royal union”, also known as Classical Yoga or simply Yoga) is one of the six orthodox (astika) schools of Hindu philosophy, outlined by Patanjali in his Yoga Sutras. Raja yoga is concerned principally with the cultivation of the mind using meditation (dhyana) to further one’s acquaintance with reality and finally achieve liberation.

The eight “limbs” or steps prescribed in the second pada of the Yoga Sutras are: Yama, Niyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana and Samadhi.

Ashtanga yoga consists of the following steps: The first five are called external aids to Yoga (bahiranga sadhana)

Yama refers to the five abstentions. These are the same as the five vows of Jainism.
Ahimsa: non-violence, inflicting no injury or harm to others or even to one’s ownself, it goes as far as nonviolence in thought, word and deed.
Satya: truth in word & thought.
Asteya: non-covetousness,, to the extent that one should not even desire something that is not his own.
Brahmacharya: abstain from sexual intercourse; celibacy in case of unmarried people and monogamy in case of married people. Even this to the extent that one should not possess any unholy thoughts towards any other man or woman except one’s own spouse. It’s common to associate Brahmacharya with celibacy.
Aparigraha: non-possessiveness
Niyama refers to the five observances
Shaucha: cleanliness of body & mind.
Santosha: satisfaction; satisfied with what one has..
Tapas: austerity and associated observances for body discipline & thereby mental control.
Svadhyaya: introspection
Ishvarapranidhana: surrender to (or worship of) God.
Asana: Discipline of the body: rules and postures to keep it disease-free and for preserving vital energy. Correct postures are a physical aid to meditation, for they control the limbs and nervous system and prevent them from producing disturbances.
Pranayama: control of breath. Beneficial to health, steadies the body and is highly conductive to the concentration of the mind.
Pratyahara: withdrawal of senses from their external objects.
The last three levels are called internal aids to Yoga (antaranga sadhana)

Dharana: concentration of the citta upon a physical object, such as a flame of a lamp, the mid point of the eyebrows, or the image of a deity.
Dhyana: steadfast meditation. Undisturbed flow of thought around the object of meditation (pratyayaikatanata). The act of meditation and the object of meditation remain distinct and separate.
Samadhi: oneness with the object of meditation. There is no distinction between act of meditation and the object of meditation. Samadhi is of two kinds:
Samprajnata Samadhi conscious samadhi. The mind remains concentrated (ekagra) on the object of meditation, therefore the consciousness of the object of meditation persists. Mental modifications arise only in respect of this object of meditation.
This state is of four kinds:
Savitarka: the Citta is concentrated upon a gross object of meditation such as a flame of a lamp, the tip of the nose, or the image of a deity.
Savichara: the Citta is concentrated upon a subtle object of meditation , such as the tanmatras
Sananda: the Citta is concentrated upon a still subtler object of meditation, like the senses.
Sasmita: the Citta is concentrated upon the ego-substance with which the self is generally identified.
Asamprajnata Samadhi supraconscious. The citta and the object of meditation are fused together. The consciousness of the object of meditation is transcended. All mental modifications are checked (niruddha), although latent impressions may continue.