Adi Shankaracharya’s concept of Advaita or absolute monism:
The Supreme Spirit or the Brahman is alone real and the individual self is only the Supreme Self and no other. Brahman is supreme intelligence, devoid of attributes, form, changes or limitations. It is self-luminous and all pervading and is without a second. The empirical world is unreal, an illusion born of ignorance. The jiva continues in Samsara only as long as it retains attachment due to ignorance or Maya. If it casts off the veil of Maya through knowledge or Jnana it will realize its identity with the Brahman and get merged into it.
(Source: Main Currents in Indian Culture - By