Step 1: Understanding Apohavāda.
Apohavāda or Apohasiddhānta is a famous Buddhist theory of meaning (semantics) particularly explained by Dignāga and Dharmakīrti. According to this theory, words signify an object not by directly denoting it, but by excluding everything else (apoha = exclusion).
Step 2: Meaning of Atadvayāvartaka.
The essence of Apohavāda is that a word means “exclusion of the other” (anyāpoha). This is expressed as Atadvayāvartaka, meaning “exclusion of the double negation.” In other words, when we say “cow,” we actually mean “not non-cow.”
Step 3: Elimination of incorrect options.
- (1) Asaṅkhyeya → Refers to countless or innumerable, not related here.
- (2) Avarṇanīya → Means indescribable, not related to Apoha theory.
- (4) Asadvayāvartaka → Incorrect term, not used in Apoha theory.
Step 4: Conclusion.
Hence, Apohasiddhānta is identified as Atadvayāvartaka.
Final Answer:
\[
\boxed{\text{The correct answer is (3) Atadvayāvartaka.}}
\]