This Hindu notion is complex.
Most often it is translated as “cosmic illusion”, yet Māyā is also the “Divine Play”, the “Universal Possibility”, and the śakti (power) of Brahman (the Absolute).

More precisely

The Sanskrit term Māyā derives from the root mā- (“to measure, to delimit, to form”), indicating a power of determination that gives shape to possibility.
It designates the power through which the Absolute (Brahman) manifests itself in a multiplicity of states, forms, and worlds.

In Advaita Vedānta, especially in Śaṅkara, Māyā is understood as the cosmic power of illusion (avidyā): it makes the phenomenal world appear as real in itself, whereas it possesses only relative reality.
It veils the non-dual nature of Brahman, producing duality (subject/object), multiplicity, time, space.

Yet Māyā is not “nothing”: it is real as manifesting power, yet unreal insofar as it has no independent existence.
Its ontological status is thus intermediate (neither absolutely real nor absolutely unreal).

Māyā is also viewed as śakti, the power of Brahman; hence, a feminine creative principle.
In Śākta and tantric currents, this dimension becomes central: manifestation is not merely illusion but divine play (līlā), expression of the infinite freedom of the Absolute.

In some interpretations, Māyā is Universal Possibility: the total set of possibilities of manifestation contained within the Infinite.
It corresponds to the principial aspect of becoming, through which all conditioned reality is made possible.

Thus, from a metaphysical standpoint, Māyā is not reducible to illusion.
She is the manifesting act of Reality, while also being that by which Reality remains veiled to beings identified with the phenomenal world.
She is simultaneously Veil and Matrix, Limitation and Possibility, principle of relativity and manifestation.

For further reading

  • Upaniṣads (especially Śvetāśvatara Up.) — Earliest scriptural sources.
  • Śaṅkara (Śaṃkarācārya), Commentaries on the Bhagavad-Gītā & Brahma-sūtra — Non-dual doctrine of Māyā–avidyā.
  • Gauḍapāda, Māṇḍūkya-kārikā — On non-duality and the illusory character of becoming.
  • Rāmānuja, Śrī-Bhāṣya — Vishnuite interpretation: relation of Māyā, manifestation, and grace.
  • Abhinavagupta — Tantric / Śaiva view of Māyā-śakti.
  • A.K. Coomaraswamy, essays — On Māyā as universal possibility and form.
  • René Guénon, Man and His Becoming According to the Vedānta — Synthetic presentation of the doctrine.