What is the meaning of Γ?

the Euler-Mascheroni constant

photon, gamma ray

Lorentz factor

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 and it represents either a voiced velar fricative: /ɣ/ or a voiced palatal fricative: /ʝ/; before velars, it represents a velar nasal: /ŋ/. It is preceded by β and followed by δ.

Source: wiktionary.org