The word is used in Surah Muzammil :
‘And recite the Qur’an in slow measured rhythmic
tone’
(Al Qur’an ; 73:4)
The Arabic word translated as ‘slow, measured rythmic’ is TARTEEL. The
tafseer of the above ayat according to Ibn Kathir is ‘recite the Qur’an slowly,
making the letters clear, for this is an assistance in understanding and pondering
the meaning of the Qur’an.’
The teaching used in this website is Hafs ‘An ‘Aasim by the way of
Shaatibiyyah.