What is the meaning of γ?

the Euler-Mascheroni constant

photon, gamma ray

Lorentz factor

a voiced velar fricative (IPA [ɣ]).

The 4th letter of the Arvanitic Albanian Greek-script alphabet.

Lower-case gamma, the third letter of the ancient Greek alphabet. Its name was γάμμα and it represented a voiced velar stop: /ɡ/; before velars, it represented a velar nasal: /ŋ/. It is preceded by β and followed by δ.

A letter of the Wakhi alphabet, written in the Latin script.

Lower-case gamma, the third letter of the modern Greek alphabet. Its name is γάμμα or γάμα. It is preceded by β and followed by δ.

Source: wiktionary.org