Ajj linguistically means raising one's voice. According to the Sharee‘ah, ‘Ajj means raising one's voice in Talbiyah.
Importance of Talbiyah is that it is one among the symbols of the Hajj. The best Hajj is the one where the Talbiyah echo’s aloud. Abu Bakr As-Siddiq(R) narrated that:The Messenger of Allah was asked: "Which Hajj is the most virtuous?" He said: "That with raised voices (Al-Ajj) and the flow of blood (of the sacrifice) (Ath-Thajj). Classed as Sahih by sheikh Albani, Jami at-Tirmidhi 827