Sangathi / sangati

Are musical phrases applied to a base phrase, and referred in the context of variations, either with subtle or gross modifications, improvisations or changes.

Saint Thyagaraja is credited with introducing sangati-s into the kriti form.

A particular variation of a phrase in a kriti or song with slight or large changes in tune and gamakas. Each phrase maybe repeated with different small or large variations or sangatis. While it is difficult to quantify change, the change is about the melodic content alongside structural many times.

Below quoted from Ramesh Mahadevan.

Sometimes, in a kriti, the first lines will be varied systematically as the singer repeats it over and over. (This happens even in some movie songs). That is, the Pallavi will be sung intentionally in different melodies as it gets repeated. The text of the line will be the same, but the music will be different. Such variations are called 'Sangatis'. These variations or Sangatis are intended by the original composer (or cleverly introduced by some other musician somewhere along the line) and are parts of the song. If you listen to a Kriti like 'Vatapi Ganapatim' in Ragam Hamsadhwani, you will notice that the singer spends a long time mulling over the first line itself. But if you paid close attention to details, the singer is in fact varying the melody of that line over and over - in other words, the singer is producing the various 'Sangati's. Sometimes, after all the variations are done, the final version of the Pallavi could sound totally different from what one started out with. In fact, usually, the final version of the Pallavi is what is the official version of the Pallavi from that point on - and this is the version that is sung after each stanza (charanam) subsequently. Even Anu pallavi can have associated Sangatis.