Indriya: 'abilities', is a name for 22, partly physical, partly mental, phenomena often treated in the Suttas as well as in the Abhidhamma. They are:
6 Bases āyatana :
1. eye: cakkhu 2. ear: sota 3. nose: ghāna 4. tongue: jivhā 5. body: kāya 6. mind: mano
Gender bhava :
7. femininity: itthi 8. masculinity: purisa 9. vitality: jīvita
5 Feelings vedanā q. v.
10. bodily pleasant feeling: sukha 11. bodily pain: dukkha 12. gladness: somanassa 13. sadness: domanassa 14. indifference: upekkhā
5 Spiritual Abilities see: bala
15. faith: saddhā 16. energy: viriya 17. awareness or mindfulness:sati 18. concentration:samādhi 19. understanding: paññā
3 supra-mundane Abilities
20. the assurance: 'I shall know what I did not yet know!': aññātañ-ñassāmīt' indriya 21. the ability of highest knowledge: aññindriya 22. the ability of him who knows: aññātāvindriya
1-5, 7-8 are physical; 9 is either physical or mental. All the rest are mental. - 14 see: upekkhā is here merely indifferent feeling = adukkha-m-asukhā vedanā i.e. 'neither pleasant nor unpleasant feeling' and not identical with that highly ethical state of equanimity = tatramajjhattatā i.e. 'keeping everywhere the middle', the equipoise of mind, also called upekkhā which belongs to the group of mental constructions sankhāra-khandha see: Tab II. - 20 arises at the moment of entering the Sotāpatti-path sotāpatti-magga 21 on reaching the Sotāpatti-Fruition sotāpatti-phala 22 at attaining the Arahat-Fruition arahatta-phala For the three last, see: ariya-puggala
The abilities, excepting 7 and 8, form one of the 24 conditions paccaya 6.
In Vibh. V all these abilities are treated in the above order, whereas see: XLVIII enumerates and explains them by way of the above indicated groups, leaving only 20-22 unexplained. See Vis XVI
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.