أَوْ تَخْصِيصُهُ إِنْ أُضِيفَ إِلَى نَكِرَةٍ، نَحْوُ: «غُلَامُ رَجُلٍ».
Translation: When attached to an indefinite noun, semantic iḍāfah makes the mudāf more specific, as in “a man’s servant.”
رَجُلٍ is indefinite: no particular man is identified. The construction does not make ghulām fully definite.
Yet it narrows the sense from “a servant” to “a servant associated with some man.” That narrowing is takhṣīṣ.