Gat in its most general sense means a fixed composition. As such, you find gats for both melodic instruments as well as rhythmic instruments like the tabla. However, the most usual use of the word implies the fixed composition for melodic instruments.
Gat is a structure very much like like the sthai in the vocal tradition. It has a fully developed cycle and is invariably accompanied by the tabla. There are two basic approaches; masitkhani and razakhani. The masitkhani gat is the basic slow gat while the razakhani is fast. In recent years, the distinction between the two styles has become blurred. Furthermore, the contemporary structure of both the fast and slow sections seems to have morphed away from the styles developed by Raza Khan and Masit Khan.
Rajeev Janardan: Raag Yaman vilambit gat
Rajeev Janardan: Raag Yaman drut gat
Gouri banerjee playing raag Madhubanti in Sarangi.
Sukhawat Hussain (Sarod) Fayyaz Khan (Tabla) 1937
Ustad Ail Akbar Khan