- (mathematics) A mathematical function formally known as the Riemann zeta function.
- Lower-case zeta, the seventh letter of the ancient Greek alphabet. Its name was ζῆτα. The sound it represented is disputed, some claim it was /zd/, others claim it was /dz/. It is preceded by ϝ and followed by η.
- Lower-case zeta, the sixth letter of the modern Greek alphabet. Its name is ζήτα and it represents a voiced alveolar fricative: /z/. It is preceded by ε and followed by η.