Nominative (rafʿ), accusative (naṣb), and genitive (jarr) are three case states of a noun. In this first class their usual signs are:
Nominative ← ḍamma: زَيْدٌ
Accusative ← fatḥa: زَيْدًا
Genitive ← kasra: زَيْدٍ
Distinguish the two: case states are grammatical functions; the vowels shown here are the case signs.