A rāg is one of the melodic modes used in Indian classical music.
A rāg uses a series of five or more musical notes upon which a melody is constructed. However, it is important to remember that the way the notes are approached and rendered in musical phrases and the mood they convey are more important in defining a rag than the notes themselves.
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 and ghazals sometimes use rāgas in their compositions.
Many Hindustani (North Indian) rāgas are prescribed for the particular time of a day or a season. When performed at the suggested time, the rāga has its maximum effect. For example, many of the Malhar group of rāgas, which are ascribed the magical power to bring rain, are performed during the monsoon. However, these prescriptions are not strictly followed, especially since modern concerts are generally held in the evening.
There has also been a growing tendency over the last century for North Indian musicians to adopt South Indian rāgas, which do not come with any particular time associated with them. The result of these various influences is that there is increasing flexibility as to when rāgas may be performed.