The third book of the sutras might also be the most esoteric. The word vibhuti means ‘power’ or ‘manifestation’ as these sutras lay out how long term and dedicated yoga practice can manifest. In this book, Patañjali defines three internal aspects of yoga – dharana, dhyana and samadhi. You might recognize these as the last three limbs of Ashtanga from book two. These can be explored by a yoga-practitioner to gain a deeper understanding of both the inner and outer world.
The concept of siddhi is also defined in this book as the extraordinary skills that a person can gain through continued practice of yoga. One should note though, that the sutras define siddhis both as achievements of yogic practice, but also as possible impediments to the self-realization and liberation of kaivalya.