In plain words
Rāja Yoga is simply the dhyāna we practise to recognise the principle of the jīva and of Brahman and, within the mind, to make the jīva principle one with the principle of the Paramātma. Rāja Yoga is a means of knowing oneself. The chief aim in Rāja Yoga is puṣṭi, santuṣṭi, Śānti, kānti; through them, by the joining of thought, word and deed, not to desire in the least what belongs to others; and, keeping the senses under control, to spend one's life always in Śānti and happiness. This Rāja Yoga does not call for the renunciation of all attachment. The chief principle of Rāja Yoga is just this: to stay in society itself, carry out one's family responsibilities and duties, and follow the truth that all karma is done to please God. This yoga is the noblest of all the yogas. In it we are to reach this goal leading a peaceful life on the proper path, with no troubles of any kind. It is supremely noble and has made the royal road plain; that is why the name Rāja Yoga is a name true to its meaning.
Because the eight limbs are joined in this yoga, Rāja Yoga itself is also called Aṣṭāṅga Yoga
Because control of the senses is the chief principle in this yoga, it has another name, Saṃyama Yoga. Because it makes plain the principle of the jīva and Īśvara, it has yet another name too, Dhyāna Yoga. Because the eight limbs are joined to this yoga, it has another name as well, Aṣṭāṅga Yoga. These are the eight limbs: yama, niyama, āsana, prāṇāyāma, pratyāhāra, dhāraṇā, dhyāna and samādhi.
‘Yama’ means speaking Satya, joined with Ahiṃsā
Of these, the first is yama. ‘Yama’ means speaking Satya, joined with Ahiṃsā.