Definition of "zeta"

The sixth letter of the modern Greek alphabet (Ζ (Z), ζ (z)) preceded by epsilon (Ε (E), ε (e)) and followed by eta, (Η (I), η (i)); or the seventh letter in the ancient Greek alphabet, in which it is preceded by digamma (Ϝ (W), ϝ (w))  examples

(mathematics) A mathematical function formally known as the Riemann zeta function.  examples