Tertia means harmonising a melodic line by adding parallel 3rds to it.
Mozart-Allegro D major
Composition with extensive use of Tertia Quiescenza, that is direct motion 3rds to a melodic bass with a Quiescenza voice (pedal tone) on tonic or/and dominant added. Mozart embellishes this voice with an acciacatura.
Also check ‘Mama’ by P.I. Tschaikowsky. Same technique. When ascending the scale with Tertia Quiescenza, a progression from Tritto 188.8.131.52 to Finale 184.108.40.206 is almost automatically generated (when descending: Reverence 220.127.116.11 followed by Prinner 18.104.22.168).