It is the atmospheric boundary between the troposphere and stratosphere.
The tropopause is the lowest level (about 16 km near equator and 10 km near poles) at which the rate of decrease of temperature with height (lapse rate, usually 6 deg/km) decreases to 2 degree Centigrade per km. The jet stream and fronts introduce complex tropopause structure e.g 'tropause funnel' (a bowl-shaped lowering of the tropopause). The dynamical behaviour of the tropopause plays important role in the vertical transport of trace gases.
GES DISC Datasets
Other sources for data