The term is commonly translated in reference to the Quran as recitation, "in proper order" and "with no haste".
[1] It is also the term used to define the rules explaining proper recitation of the Qur'an in the manner that Gabriel revealed it to Muhammad.
The fourth caliph, Ali ibn Abi Talib, said that tarteel is delivering words according to their makharij (outlets for sound or intonations).
Saying the words clearly and slowly and reciting with understanding and uttering the contents correctly is of prime importance.
According to him, "Following the middle path is a virtue" or in Arabic: خير الأمور أوسطها (Khayru l-umūri awsaṭuhā).