Dear Sir, the answer is available in net but I am writing of my own so that it makes you clear.

In a single sentence we can sum up that gharana is a style of music or school of music. In India there are many gharanas. Each gharana has its own specialty. Few of the popular gharanas in India are Agra gharana, Agra, Benaras gharana, Benaras, Bhendibazaar gharana, Bishnupur gharana, Bengal, Delhi gharana, Gwalior gharana, Gwalior, Indore gharana, Jaipur-Atrauli gharana, Kirana gharana, Mewati gharana, Patiala gharana, Rampur-Sahaswan gharana, Sham Chaurasia gharana, Punjab (Pakistan)
Every Gharana has its own distinct features. The main area of difference between Gharanas is the manner in which the notes are sung. The concept of a Guru- Shishya leads to the development of Gharanas. The Gharanas emerge from the creative style of a genius, who gives existing structures a totally new approach, form and interpretation. The new approach, form and interpretation apply to include the tone of ...more

Courtesy google: cultural India:
There is a rich tradition of Gharanas in classical Hindustani music. The music Gharanas are also called styles. These schools or Gharanas have their basis in the traditional mode of musical training and education. Every Gharana has its own distinct features. The main area of difference between Gharanas is the manner in which the notes are sung. The concept of a Guru- Shishya leads to the development of Gharanas. The Gharanas emerge from the creative style of a genius, who gives existing structures a totally new approach, form and interpretation. The new approach, form and interpretation apply to include the tone of the voice, the pitch, the inflexions and the intonations, and the specific application of the various nuances. Let\'s have a quick look at popular Gharanas of Hindustani classical music.

Gwalior Gharana - This is the oldest among all the Khayal Gayaki (vocal) styles. The distinctive feature of this style of singing has been noted as its ...more