Study a single sutra by selecting the pada (chapter) and then the sutra (verse).
Source: English translation from The Yoga Sutras of Patanjali (Sri Swami Satchidananda)
Ignorance is regarding the impermanence as permanent, the impure as pure, the painful as pleasant, and the non-Self as the Self.
Source: English translation from Light on the Yoga Sutras of Patanjali (B.K.S. Iyengar)
Mistaking the transient for the permanent, the impure for the pure, pain for pleasure, and that which is not the self for the self: all this is called lack of spiritual knowledge, avidya.
Source: How to Know God: The Yoga Aphorisms of Patanjali (Swami Prabhavananda, Christopher Isherwood)
To regard the noneternal as eternal, the impure as pure, the painful as pleasant and the non-Atman as the Atman -- this is ignorance.
Source: English translation of the Yoga Sutras of Patanjali (Swami Jnaneshvara Bharati)
Ignorance (avidya) is of four types: 1) regarding that which is transient as eternal, 2) mistaking the impure for pure, 3) thinking that which brings misery to bring happiness, and 4) taking that which is not-self to be self.