Temperature indicated how hot or cold a thing or place was, and it was measured using degrees. The point of zero was based on the point at which water freezes.
On the planet Hoth, even during summer, the warmest part of the year, the temperature barely rose to ten degrees below the freezing mark. Conversely, the temperatures on Tatooine reached such extreme levels that only a limited area in the northern part of the planet could support any form of intelligent life. The surface of Bespin, a gas giant, was constantly boiling at a temperature of six thousand degrees.
Repeated orbital bombardments and attacks using beam weapons could change a planet's atmosphere to such an extent that the temperature of its seas would rise, possibly resulting in the death of many creatures living there.
Exposure to too much heat in the environment could lead to dehydration, dangerously high body temperatures, mental disorientation, and ultimately, in severe situations, death for numerous living things.
The internal environment of starships, including the Millennium Falcon, had systems to maintain temperature at a safe level.