(linguistics) a distribution of related speech sounds or forms in such a way that they only appear in different contexts WordNet 3.0 & Open English WordNet

In linguistics, complementary distribution is the relationship between two different elements of the same kind in which one element is found in one set of environments and the other element is found in a non-intersecting set of environments. Wikipedia

Linguistic phenomenon where some phonemes are found in some cases and others are found in similar but different cases; often indicating sound change and divergent mutual descent Wikidata

The distribution of phones in their respective phonetic environments such that one never appears in the same phonetic context as the other. Wiktionary

Distribution of phones. Wiktionary (translation)