The gazal is a poetic form consisting of rhyming couplets and a refrain, with each line sharing the same meter. A ghazal may be understood as a poetic expression of both the pain of loss or separation and the beauty of love in spite of that pain. The form is ancient, originating in 6th century Arabic verse. It is derived from the Arabian panegyric qasida. The structural requirements of the ghazal are similar in stringency to those of the Petrarchan sonnet. In its style and content it is a genre which has proved capable of an extraordinary variety of expression around its central themes of love and separation. It is one of the principal poetic forms which the Indo-Perso-Arabic civilization offered to the eastern Islamic world.
Important poets of Urdu ghazal
In Urdu some important and respected ghazal poets are Wali, Aatish, Mir Taqi Mir, Mirza Rafi Sauda, Mirza Ghalib, Zauq, Dard, Daagh, and Jigar Moradabadi. Post-partition poets include Firaq Gorakhpuri, Majrooh Sultanpuri, Faiz Ahmed Faiz, Jaun Elia, Habib Jalib, Munir Niazi, Jan Nisar Akhtar, Shakeb Jalali, Parveen Shakir, Tanwir Phool, Qamar Jalalabadi, Qateel Shifai, Aghar Gondvi, Nasir Kazmi, Ahmed Faraz, Makhdoom Mohiuddin, Sahir Ludhianvi, Nida Fazli, Gulzar, Ali Arman, Vikram Singh, Raees Warsi, Mir Dard, Hasrat Mohani, Momin Khan Momin, Altaf Hussain Hali
singerspassion 
How could you miss Saigol and Pankaj
Thanks for your interest first Syed A. Ehtisham.. Pankaj udhas already mention there and in my point of view the legend Saigal ji was a versatile singer I can not recognise him in ghazal mehfil only.