What is the meaning of Ζ?

A mathematical function, formally known as the Riemann zeta function.

Symbol used to represent zoophilia and zoophiles.

The 10th letter of the Albanian alphabet, called Arvanitic or Arvanitika and written in the Greek script. ζ, Ζ

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.

Source: wiktionary.org