SB 1.2.11

vadanti tat tattva-vidas
 tattvaṁ yaj jñānam advayam
brahmeti paramātmeti
 bhagavān iti śabdyate
Word for word: 
vadanti — they say; tat — that; tattva-vidaḥ — the learned souls; tattvam — the Absolute Truth; yat — which; jñānam — knowledge; advayam — nondual; brahma iti — known as Brahman; paramātmā iti — known as Paramātmā; bhagavān iti — known as Bhagavān; śabdyate — it so sounded.
Translation: 
Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramātmā or Bhagavān.
Purport: 

The Absolute Truth is both subject and object, and there is no qualitative difference there. Therefore, Brahman, Paramātmā and Bhagavān are qualitatively one and the same. The same substance is realized as impersonal Brahman by the students of the Upaniṣads, as localized Paramātmā by the Hiraṇyagarbhas or the yogīs, and as Bhagavān by the devotees. In other words, Bhagavān, or the Personality of Godhead, is the last word of the Absolute Truth. Paramātmā is the partial representation of the Personality of Godhead, and impersonal Brahman is the glowing effulgence of the Personality of Godhead, as the sun rays are to the sun-god. Less intelligent students of either of the above schools sometimes argue in favor of their own respective realization, but those who are perfect seers of the Absolute Truth know well that the above three features of the one Absolute Truth are different perspective views seen from different angles of vision.

As it is explained in the first śloka of the First Chapter of the Bhāgavatam, the Supreme Truth is self-sufficient, cognizant and free from the illusion of relativity. In the relative world the knower is different from the known, but in the Absolute Truth both the knower and the known are one and the same thing. In the relative world the knower is the living spirit or superior energy, whereas the known is inert matter or inferior energy. Therefore, there is a duality of inferior and superior energy, whereas in the absolute realm both the knower and the known are of the same superior energy. There are three kinds of energies of the supreme energetic. There is no difference between the energy and energetic, but there is a difference of quality of energies. The absolute realm and the living entities are of the same superior energy, but the material world is inferior energy. The living being in contact with the inferior energy is illusioned, thinking he belongs to the inferior energy. Therefore there is the sense of relativity in the material world. In the Absolute there is no such sense of difference between the knower and the known, and therefore everything there is absolute.