Tamyīz is an indefinite noun clarifying an unclear quantity or sentence relation.
The book gives number, volume, weight, area and related measures.
A material can also be clarified without an explicit measure; in some such uses genitive iḍāfa is more common.
Sentence-level tamyīz clarifies the relation itself, as in «طَابَ زَيْدٌ نَفْسًا».
Distinguish it from ḥāl, adjectives, and direct objects.