Vadi, in both Hindustani classical music

Hindustani classical music

Hindustani classical music is the Hindustani or North Indian style of Indian classical music found throughout the northern Indian subcontinent. The style is sometimes called North Indian Classical Music or Shāstriya Sangeet...

 and Carnatic music

Carnatic music

Carnatic music is a system of music commonly associated with the southern part of the Indian subcontinent, with its area roughly confined to four modern states of India: Andhra Pradesh, Karnataka, Kerala, and Tamil Nadu...

, is the dominant swara

Swara

The seven notes of the scale , in Indian music are named shadja, rishabh, gandhar, madhyam, pancham, dhaivat and nishad, and are shortened to Sa, Ri or Re , Ga, Ma, Pa, Dha, and Ni and written S, R, G, M, P, D, N. Collectively these notes are known as the sargam...

 (musical note) of a given raga

Raga

A raga is one of the melodic modes used in Indian classical music.It is a series of five or more musical notes upon which a melody is made...

 (musical scale). "Vadi is the most sonant or most important note of a Raga." It does not refer to the most played note but it rather refers to a note of special significance.
It is usually the swara which is repeated the greatest number of times, and often it is the swara on which the singer can pause for a significant time.

Vadi swara, along with the Samvadi swara of a raga, usually brings out the uniqueness of the raga and its bhava (mood) and rasa (emotion).