Varnam is a form of song in the Carnatic music repertoire. Carnatic music (also spelled Karnatak music or Karnatik music, and originally called Karṇāṭaka sangīta or Karṇāṭaka sangītam in India A varnam is a relatively long piece and can range from 30 minutes to up to nearly an hour or 40-50 min. It is usually set to Aadi or Ata tala. It is the center piece in a recital of music or dance. The lyrics are simple and consist mostly of long syllables and swara phrases of various lengths which bring out the essential features of the raga. Rāga ( Sanskrit, lit "colour" or "mood" or rāgam in Carnatic music) refers to melodic modes used It has two types: Taana varnam and Pada varnam.
Varnams are considered vocal exercises in a particular raga. Rāga ( Sanskrit, lit "colour" or "mood" or rāgam in Carnatic music) refers to melodic modes used The patterns in a varnam are considered to be characteristic patterns of a particular raga or scale. Varnams are considered the most complex of the vocal exercises in Carnatic Music. They are designed to help develop voice culture and proper control of rhythm. Indeed, varnams are often practiced in double and triple speeds and proper rhythmic control (tala) must be kept.
Named for it's thanam-like rhythmic qualities, tana varnams only have lyrics for the pallavi, anupallavi and charanam. Ragam Thanam Pallavi is a form of singing in Carnatic music which allows the musicians to improvise to a great extent In Indian classical music pallavi is the thematic line of a song In Indian classical music, the anupallavi comes after the Pallavi and is usually the second section of any composition Charanam, meaning foot is usually the end section of a composition which is sung after the Anupallavi. 
With rhythmic elements like a padam, pada varnams are generally sung to accompany South Indian classical dance, including bharatanatyam. The Indian numbering system, used today in India, Pakistan, Bangladesh, Nepal and Myanmar (Burma is based on grouping by two Bharatanatyam (பரதநாட்டியம்is a classical Dance form originating in Tamil Nadu,  Unlike the tana varnam which only has lyrics for the pallavi, anupallavi and charanam and swarams for the rest of the sections a pada varnam also have lyrics that correspond to the muktayi and chitta swaras of the varnam, so generally, pada varnams contain more lyrical content than a tana varnam. In Indian classical music pallavi is the thematic line of a song In Indian classical music, the anupallavi comes after the Pallavi and is usually the second section of any composition Charanam, meaning foot is usually the end section of a composition which is sung after the Anupallavi.  The swaras in this type of varnam are suitable for intricate footwork. for the town in Nepal see Swara Nepal The notes or swaras, of Indian music are shadja rishabh gandhar madhyam pancham dhaivat and nishad  Padajathi varnams are simply pada varnams that also contain jatis in it, making it again more suitable for South Indian classical dance. 
The varnam is subdivided into several sections:
Generally, a varnam is sung as follows:
Repeat, then Pallavi sung in triple speed, or in original speed.
There are generally 3-5 swara groups in every varnam. In a concert, the entire charanam section is sung at approximately 1. 5 speed. Sometimes when repeating the Pallavi the Annupallavi and Muktayi Swarams are repeated in double or triple speed.
Varnams are generally sung in 2 varieties of talas, or metric systems, Adi Tala (8 beat cycle) and Ata Tala (14 beat cycle), where Ata Tala varnams are generally more complicated and advanced.
Famous adi tala tana varnams include "Sāmi Ninne" in Sree Raga, "Evvari Bodhana" in Abhogi Raga and "Valachi Vacchi" in a navarāgamālika, or 9 ragas, similar to Ragamalika which literally translates to a "garland of ragas" . The Arabhi Raga Varnam is supposed to be the only longest piece with janttai and tattu prayogas. Famous ata tala varnams are "Viriboni" in Bhairavi Raga, and "Nera Nammi" in Kānada Raga. A famous adi tala Pada Varnam is "Chalamela" in Nāttakurinji Raga.