The stratosphere is the second layer of our planet’s atmosphere, wedged between the troposphere (1st layer) and mesosphere (3rd layer).  It reaches roughly from altitudes of 10km to 50km.  These boundaries are set by reversals in the temperature grade.  In the troposphere, as altitude increases temperature decreases, however, in the stratosphere the reverse is true.  This is because ozone builds up at the outer extent of the stratosphere capturing UV radiation from the sun, and thus warming up.  .  Then in the mesosphere temperature starts decreasing again with altitude gain.  Commercial airliners and military planes often operate at altitudes around 9-12km because of the unique turbulence free nature of the stratosphere.  The stratosphere supports bacterial life, so it is considered part of the biosphere.  There have even been reports of birds flying in the stratosphere and over mount Everest, whose peak is around 9km.

The stratosphere is also considered near-space, not actual space.  It is also possible to send a camera payload up to the stratosphere using a a large helium balloon for relatively low cost like these MIT kids did…