Error is false knowledge stemming from the incorrect apprehension [of something].

Bryant Commentary:

Patañjali now proceeds to the second of the five different types of vṛttis, error. Vyāsa defines error as considering something to be what it is not, atad-rūpa, a state that can be subsequently removed by true knowledge of the actual nature of the thing in question. As an example he gives the perception of two moons. After consuming alcohol, a person may see double. This error of perception nonetheless produces a vṛtti in the mind of this person, but this vṛtti differs from vṛttis produced by valid sources of knowledge insofar as the seeing of two moons is an apparent perception that can be contradicted and dismissed by a later accurate perception that there is only one moon in reality, whereas valid knowledge cannot be contradicted. Vijñānabhikṣu notes that error is the result of the superimposition of wrong knowledge, mithyā-jñānam, onto an object (in our example, an extra moon is superimposed onto the actual solitary one).

The classical example of error, especially among the followers of Vedānta, is mistaking a rope for a snake: If one happens upon a rope on the path as one is walking home at dusk, and imagines it to be a snake, one is superimposing the form of a snake upon something that is not a snake. This is error according to the Yoga school (different schools of philosophy hold differing views on what constitutes error). The Nyāya school, which especially concerns itself with epistemology, the methods of accurate knowledge, has a similar definition, giving as an example of error considering mother-of-pearl as containing silver. (Specifically, Nyāya defines knowledge, pramā, as apprehending an object as it is, correctly identifying the attribute of that object, and error as the opposite, considering an object to have an attribute that in fact it does not have—the mother-of-pearl does not contain silver.) Vyāsa considers error to be essentially the five kleśas, the impediments to the practice of yoga: ignorance (avidyā), ego, attachment, aversion, and clinging to life. However, avidyā is the root of the other kleśas (II.4), and we will argue in II.5 that it is a fundamentally deeper and more subconscious type of ignorance than the surface-level error represented in this sūtra by viparyaya.

Viparyaya Or Illusion Is False Knowledge Formed Of A Thing As Other Than What It Is.

Misperception is false knowledge, not based on what actually is.

Misconception is an illusory knowledge founded on an unreliable appearance lacking its own inherent integrity.

Wrong knowledge is a false conception of a thing whose real form does not correspond to such a mistaken conception.

Taimini Commentary:

The second type of Vrtti called Viparyaya is also based on some kind of contact with an external object but the mental image does not correspond with the object. The examples usually given to illustrate this kind of Vrtti such as a mirage in a desert may give the impression that it is very rare but this is not a fact. Cases of Viparyaya are very frequent. Wherever there is lack of correspondence between our conception of a thing and the thing itself we have really an instance of Viparyaya. But it should be remembered that in Viparyaya we are not concerned with the correctness or definiteness of our mental impressions but only with the correspondence between the object and the mental image formed in our mind. In partial darkness our impression of an object may be blurred but if it corresponds with the object it is not a case of Viparyaya.

Illusory or erroneous knowledge is based on non-fact or the non-real.

Iyengar Commentary:

Perverse, illusory or wrong knowledge is caused by error or misconception, or by mistaking one thing for another. It is based on the distortion of reality. Wrong understanding and false conceptions generate wrong feelings and taint the consciousness. This hinders the sadhaka in his efforts to experience the seer, and may create a dual or split personality.

Misconception occurs when knowledge of something is not based upon its true form.

Satchidananda Commentary:

 In the twilight you see a coiled rope and mistake it for a snake. You get frightened. There is no snake there in reality. There is a false understanding. But still it created a terror in your mind. It is not only valid knowledge that creates thought waves, but erroneous impressions also.

Indiscrimination is false knowledge not established in real nature.

SV Commentary:

The next class of Vrttis that arise is mistaking the one thing for another, as a piece of mother-of-pearl is taken for a piece of silver.

Unreal Cognition is the knowing of the unreal, possessed of a form not its own. Why is it not the knowing of the real ? Because the knowledge of the real removes it, inasmuch as Real Cognition has for its object a thing as it exists. Therein is seen the removal of the wrong knowledge by the right one ; as for example, the visual knowledge of two moons is removed by the perception which has for its object the thing as it really exists, the oue moon.

This it is that is the five-fold Nescience. As it is said Nescience, Egoism, Attachment, Aversion, and Love of life are the five afflictions. — 3. 2. The same are technically called respectively, darkness (tamas), forgetfulness (moha), extreme forgetfulness (mahamoha), Excessive darkness (tamisra) and blind darkness (andhatamisra).

These will be described in the context of the impurities of the mind,

~ Rāma Prasāda translation.