Samadhi is trance. Samadhi is still one process or one Anga of Yogabhyasa, of Yogic practice. Samadhi is not the ultimate goal.
Various types of Samadhi have to be practised until your Samadhi becomes longer and longer in duration, deeper and deeper in intensity, until you become well established in the practice of Samadhi. This is Raja Yoga.
So, the meaning in which different terms are used should be clear to your mind. By continuous, diligent practice of Samadhi, it becomes longer in duration, deeper in intensity, and then you become well established in that state.
Gradually you pass through different states of Samadhi and you ultimately reach a state of Samadhi where there is absolutely no movement of the mind at all. The mind comes to a total standstill and there is not even metaphysical movement. There is not even the consideration of the Absolute, that it is Sat, that it is Chit, that it is Ananda, that it is beyond time, space and causation, that it is beginningless and endless. Even these considerations are not present any longer.
In that process of holding on to the awareness of the Supreme, there is only Absolute Awareness. That is called Nirvikalpa Samadhi and it is when the Yogi is able to practise Nirvikalpa Samadhi for a long time that he goes beyond even Samadhi and attains to the state of Turiyatita Avastha where he obtains Kaivalya, supreme liberation, supreme independence.