Maya is illusion of reality. The definition of Maya is given by God: "Maya is present where I am not and Maya cannot be without me."
This definition is explained by Jagadguru Kripaluji by a simple example: The image of Sun in the water is illusion of Sun seen by a subject. Sun cannot be inside the water or the surface reflecting its rays; otherwise the image would not form. Maya cannot be present where God is. Maya is darkness and God is bright light.
Adi-Guru Shankaracharya propounded the Philosophy of Bramha(impersonal-self) becoming 'Self,' because of Maya. Kripaluji asks " If Bramha is affected by Maya and becomes 'Jeeva'(Self), how is it possible to really attain enlightenment? How would a soul ever be free of Maya? Even if a soul gets enlightened(becomes illuminated Bramha) the Maya can again contaminate it to become Soul.
The Vaishnava way suggests that Maya is a power of God. Jeeva(Soul) is another power of God and Maya affects a soul only until God is not realized by the Soul. It's a law that Maya cannot be present where God is present. That's why the path of Bhakti gives permamnent bliss and relief from suffering once a Bhakta attains God-realization; there is no chance of getting affected by the illusion.
Maya is inert power, whereas Jeev is conscious power of God. Maya is what attaches Jeev to the world.
Soul is of atomic size and it's proven by Veda Vyasa. Souls are of two types: One is 'Swamsha' of God and others are 'Vibhinnansha.' We are Vibhinnansha and souls like Bramha, Vishnu and Mahesh and all incarnations of Shri Krishna are Swamshas--they have much power and we have a very little power.