Hi.

Generally, solar astronomers define solar flares as intense brightenings in loops in the Sun's lower corona (the corona is the Sun's atmosphere), so usually below 100,000 km or so from the solar surface (that is still pretty big compared to Earth, which has a diameter a bit under 13,000 km!). They give off UV, X-rays and even sometimes gamma rays we can observe from far away. They reach temperatures of over 20 million degrees C (over 36 million F), and sometimes as high as 100 million degrees C (180 million F) - so very, very hot!

However flares can also accelerate particles, like electrons, out into the solar system. They are also sometimes associated with Coronal Mass Ejections - explosions in which the Sun shoots giant magnetic bubbles that reach the outer limits of the solar system.

Cheers,Terry