Enlightenment is a modern term, a general word that means awareness through knowledge. Hence, it can mean a number of things depending upon what one means by knowledge. It is a loosely used word and can mean the knowledge that comes through a discerning intellect, like the Sankhya and the Buddhi Yoga, to the knowledge that arises through an identification with the true Self, Atmagyan.
The realisation of the psychic being means the realisation of the One Self in its individual mode of manifestation. The Divine Self is one, but it manifests itself differently through each individual soul. Thus, the realisation of the psychic being makes us conscious of the Divine Will in us, of the Divine Purpose in the individual, the Work one is here to do.
Self-realisation is the realisation of the One Universal Self that is the same everywhere and in everything. It brings the sense of Unity and Oneness behind all the diversity of creation.
Brahman realisation is to realise the One Self in all its various fourfold modes and various aspects such as Saguna, Nirguna, Paratpara, etc. It brings to us the realisation of the Divine in all the different ways of His Being within as well as outside creation.
Affectionately,
Alok Da
