Thaat is a system of classification of the ragas in different groups.
Presently, in Hindustani classical music, 10-Thaat classification has been adopted. According to V.N Bhatkhande, one of the most important musicologists in the field of North Indian classical music, each one of the several traditional ragas is based on, or is a variation of 10 basic thaats or musical scales or frameworks. A thaat can only be sung in aaroha as the notes are composed in the ascending order.
A thaat should have seven notes out of the 12 notes (7 Suddha Swaras and 5 Vikrata Swaras) and they should necessarily be placed in an ascending order. The 10 thaats are: Bilawal, Khamaj, Kafi, Asavari, Bhairavi, Bhairav, Kalyan, Marwa, Poorvi and Todi. Thaat has no emotional quality unlike raga and it is not sung. The ragas produced from the thaat are sung.