Tarteel is an Arabic word that refers to recitation of the Quran slowly with rhythmic tones.
Some believe that Tarteel describes the recitation of the Quran in the way Hazrat Jibrael (Angel Gabriel) recited it to the Holy Prophet (PBUH).
In the following footage, Mahmoud Yusuf recites verses 1 to 11 of Surah Al-Mulk (67th chapter) of the Quran in Tarteel.