There is a concept of avidya in Vedanta. It can be understood at two levels, individual and universal. At the individual level, it is named as vasanas or samskaras. At the universal level, it is called Maya. Maya also means as something which is not. So, this Maya/vasanas/avidya is actually not real, rather temporary and therefore illusory. This avidya is also known as avyakta (अव्यक्त नाम्नी परमेश शक्ति: अनादि अविद्या त्रिगुणात्मिका परा). This is supported by Vivekachudamani.
This has been my understanding for quite some time, until it has been rocked by Adhyas Bhashya of Brahma Sutra.
Be that as it may, this book prompted me to read the Bhashya on Gita by Shankaracharya. It has helped me to understand the concepts to a certain extent. I write here a brief account of what I have learnt.
Chapter 13 of Gita Bhashya
Lord Krishna talks about two prakriti of Ishwara in Chapter 7, one is para prakriti and another is apara prakriti.
Apara prakriti is trigunatmika, composed of three gunas. It is eightfold. It is apara because it is the cause of samsara.
Para prakriti is jivabhuta, kshetrajna lakshana and ishwaratmika.
Through these two prakritis, Ishwara is the genitor, sustainer and destroyer of the samsara.
Further, Shankara says that Prakriti is trigunatmika, sarva kaarya (body) karana (thirteen instruments, chapter 13.20) vishaya parinataya. Thus, it is clear that prakriti word is used in the sense of apara prakriti.
He further says avidyakrit upadhi and Ishwar Kshetrajna ektvadarshi. It means that upadhi of kshetrajna is created by avidya. And also, kshetrajna and Ishwara are same.
अविद्या मात्रम् संसारम् (This samsara is avidya only). न क्षेत्रज्ञस्य केवलस्य —अविद्या तत कार्यम् च (in only Kshetrajna, there is neither avidya nor its effect).
न ही ऊषर देशम् स्नेहेन पंकी कृतम् शक्नोति मरीचि उदकम् तथा अविद्या क्षेत्रज्ञस्य न किंचित कर्तुम् शक्नोति. Just as the water of mirage cannot wet the sand, avidya cannot do anything to kshetrajna. Thus, the water of mirage, avidya, kshetra cannot affect kshetrajna on which it is imagined.
संसार संसारिनो: अविद्या कल्पितत्व उपपत्य. Both samsara and samsaritva are imagined due to avidya.
Anything which is knowable has the characteristics of Kshetra. ज्ञेयस्य क्षेत्र धर्मत्वाद्.
Mahabhuta are also called sukshma bhoot. They are called so as everything is made up of them.
अहंकार: महाभूत कारणम् —-अहंकार कारणम् बुद्धि: –तत कारणम् अव्यक्तम्—अव्याकृतम् ईश्वर शक्ति: ‘मम माया दुरत्यया इति’ उक्तम् .
If we compare it with 7.4, we get to know, मनस: कारणम् अहंकारो, (बुद्धि = महत्) इति अहंकार कारणम्, अहंकार इति अविद्या संयुक्तम् अव्यक्तम्.
Thus, a sequence can be found. Mind and mahabhoot have their cause in ahamkar, (buddhi=mahat) is the cause of ahamkara. Avyakta is the cause of (buddhi = mahat). And what is avyakta? It is Ishwara’s shakti Maya. So, Avyakta and maya are synonymous.
The definition of Kshetra in 13.6 includes the word avyakta and eva. By this, it is clear that kshetra is same as apara prakriti or simply prakriti and it includes avyakta. Since buddhi emanates from avyakta therefore entire kshetra comes from avyakta.
So, basically, Kshetra = ashtadha bhinna prakriti = apara prakriti.
Jneya (13.13 onwards) is basically Kshetrajna in its real essence.
यथा रज्जु आदि सर्प आदि मिथ्या कल्पितस्य . Kshetrajna is the source, sustainer and destroyer of kshetra.
तत्र सप्तमे ईश्वरस्य द्वे प्रकृती उपन्यस्ते परा अपरा क्षेत्र क्षेत्रज्ञ लक्षणे . These two are the yoni of everything.
प्रकृतिम् पुरुषम् च एव ईश्वरस्य प्रकृती/ तौ प्रकृती पुरुषौ उभौ अपि अनादि विद्धि .
प्रकृति : ईश्वरस्य विकार कारण शक्ति :—त्रिगुणात्मिका माया .
पुरुष: जीव: क्षेत्रज्ञ :भोक्ता इति पर्याय :.
Thus, we get to understand:-
Parakriti = Apara prakriti = kshetra = Maya = Avyakta
Purush = Para prakriti = kshetrajna = Jiva = Bhokta
What is the nature of union of kshetra and kshetrajna? Their nature is that of adhyas. क्षेत्रम च माया निर्मित हस्ति, स्वप्न दृष्ट वस्तु, गंधर्व नगर आदि वद असद, सद इव अवभासते . This kshetra is asad like elephant created by maya or like thing or city seen in dream, but it appears like sad.
जन्म कारणम् च अविद्या निमित्तक: क्षेत्र क्षेत्रज्ञ संयोग:. The reason of birth is the union of kshetra and kshetrajna through avidya.
The word atman is used sometimes as jiva/ kshetrajna. One needs to be careful. देह इंद्रिय मन बुद्धि अव्यक्त आत्मन: अपेक्ष्य परमेश्वर:. So, parameshwar is beyond avyakta and atman. So, here the meaning of atman has to be kshetrajna.
प्रकृत्या प्रकृति: भगवतो माया त्रिगुणात्मिका। माया तु प्रकृति विद्यात्। प्रकृत्या महत् आदि कार्य कारण आकार परिणतया.
Prakriti = Maya = Apara prakriti = Avyakta
तथा आत्मानम् क्षेत्रज्ञ अकर्तारम् सर्व उपाधि विवर्जितम .
Atman = kshetrajna = jiva = pratyagatma.
यथा सर्व गतम् व्यापि सत सौक्ष्म्यात् सूक्ष्म भावाद आकाशम् खं न उपलिप्यते/ न संबद्ध्यते======== तथा =======सर्वत्र अवस्थितो देहे आत्मा न उपलिप्यते . Just as space is not attached, like that even though being everywhere in the body (dehe), (atma = kshetrajna=jiva) is not attached.
13.34 Most conceptual
भूतानाम् प्रकृति: अविद्या लक्षणा अव्यक्ताख्या.
Avyakta = avidya = prakriti = (maya) = (kshetra)
This last line reinforces the understanding that I had. And that is that avidya and avyakta are same. However, Shankara says that the prakriti that is named as avyakta is having the attribute of avidya, i.e avidya lakshana.