Rāga refers to melodic modes used in Indian classical music.[1] It is a series of five or more musical notes upon which a melody is made. In the Indian musical tradition, rāgas are associated with different times of the day, or with seasons. Indian classical music is always set in a rāga. Non-classical music such as popular Indian film songs or ghazals sometimes use rāgas in their compositions.

The word "raga" first occurs in the Brihaddeshi of Matanga (circa second century AD[2] or 5th to 7th century[3]), where he describes it as "a combination of tones which, with beautiful illuminating graces, pleases the people in general". The term raga was defined by Joep Bor of the Rotterdam Conservatory of Music as "tonal framework for composition and improvisation."[4] Nazir Jairazbhoy, chairman of UCLA's department of ethnomusicology, characterized ragas as separated by scale, line of ascent and descent, transilience, emphasized notes and register, and intonation and ornaments.

Nature of rāga
Raga Shree recital to Krishna and Radha, Ragamala paintings, 19th century

योऽसौ ध्वनिविशेषस्तु स्वरवर्णविभूषितः ।
रञ्जको जनचित्तानां स च राग उदाहृतः ।।

"That which is a special dhwani (tune), is bedecked with swara (notes) and varna and is colorful or delightful to the minds of the people, is said to be rāga" - Matanga in the Brihaddeshi.

The basic mode of reference in modern Hindustani practice (known commonly as the shuddha - basic - form) is a set which is equivalent to the Western Ionian mode (the major scale) — this is called Bilawal thaat in Hindustani music (the Carnatic analogue would be Sankarabharanam). In both systems, the ground (or tonic), Shadja, Sa, and a pure fifth above, Pancham, Pa, are fixed and essentially sacrosanct tones. In the Hindustani system, in a given seven-tone mode, the second, third, sixth, and seventh notes can be natural (shuddha, lit. 'pure') or flat (komal, 'soft') but never sharp, and the fourth note can be natural or sharp (tivra) but never flat, making up the twelve notes in the Western equal tempered chromatic scale (Western enharmonic pitch equivalences like, for example, A♯ and B♭ do not apply; e.g. Re tivra may, to a Western musician appear enharmonic to Ga shuddha in that system, but in practice is not.) A Western-style C scale could therefore theoretically have the notes C, D♭, D, E♭, E, F, F♯, G, A♭, A, B♭, B.

The Carnatic system has three versions — a lower, medium, and higher form — of all the notes except Sa, Ma and Pa. Ma has two versions (lower and higher), while Sa and Pa are invariant. Rāgas can also specify microtonal changes to this scale: a flatter second, a sharper seventh, and so forth. Tradition has it that the octave consists of (a division into) 22 microtones ("śrutis"). Furthermore, individual performers treat pitches quite differently, and the precise intonation of a given note depends on melodic context. There is no absolute pitch (such as the modern western standard A = 440 Hz); instead, each performance simply picks a ground note, which also serves as the drone, and the other scale degrees follow relative to the ground note. The Carnatic system embarks from a much different shuddha (fundamental) scalar formation, that is, shuddha here is the lowest-pitched swara.

By comparison, using the common tonic "C" for a western musician: