The word “scale”, means an ordered presentation of notes abstracted from any melody, put in a particular order, may be in the ascending order.In South Indian music, it will be in terms of svarasthaanas. If we say C scale or D scale, they are just that set of seven notes because they just take part in melody. In the 72 - mela scheme, all the 72 are scales.
Scales may be having seven, six or five notes, put in order. Modal shift of tonic is the process by which the tonic or the Aadhara sadja is shifted from svara to svara, keeping the sequence of the intervals of the original scale in tact. This process gives new scale. In common music language this process is known as the Grahabhedam. In ancient tamil music, this process was known as Kural tiribu, Pannuppeyarttal and Paalai Pannal.