Tarteel means "Recitation." It is used in Al-Qur'an in Surah Muzammil, verse 4, as Allah s.w.t  instructs the Prophet by saying-

"and recite the Qur'an in slow measured rhythmic tones"

The Arabic for "slow, measured rythmic tones" is tarteel. Tarteel is the term used to define the rules that explain how to recite the Qur'an in the way and manner that the angel Jibril (a.s) to our beloved Messenger (s.a.w.).

Tajweed means "Improving," or "to make something better." Tajweed is a manner of BEAUTIFYING the recitation of the Qur'an by reciting in a much slower manner than tarteel.

When praying, we recite with TARTEEL, not TAJWEED!

Tajweed is a form of recitation in which the rules of TARTEEL are used.

Therefore, when discussing the rules of recitation, the proper term to use is TARTEEL, for one cannot learn tajweed without first learning tarteel.

Wallahu 'alam.