Rāgas in performance 

The rag is the most important concept that any student of Indian music should understand. The Hindi/Urdu word "rag" is derived from the Sanskrit "raga" which means "colour, or passion" (Apte 1987).

It is linked to the Sanskrit word "ranj" which means "to colour" (Apte 1987).   Therefore rag may be thought of as an acoustic method of colouring the mind of the listener with an emotion.  This is fine as a general concept but what is it musically? It is not a tune, melody, scale, mode, or any concept for which an English word exists. It is instead a combination of different characteristics.   It is these characteristics which define the rāga. 

Here are the characteristics: 

There must be the notes of the rag. They are called the swar. This concept is similar to the Western solfege.

There must also be a modal structure. This is called that in North Indian music and mela in carnatic music.