What is the meaning of Ζ?

A mathematical function formally known as the Riemann zeta function.

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

The thirty-fifth letter of the Albanian alphabet, written in the Latin script. z, Z

The thirty-seventh letter of the Albanian alphabet, called Arbëreshë, Arvanitic, or Arvanitika and written in the Latin script. z, Z

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