What is the meaning of ι?

sometimes used to write the imaginary unit

the definite descriptor

Lower-case iota (ἰῶτα), the ninth letter of the ancient Greek alphabet. It represented the close front unrounded vowel /i/. It is preceded by θ and followed by κ.

The lower case letter iota (γιώτα), the ninth letter of the modern Greek alphabet. Transliterated as I or J.

Source: wiktionary.org