What is the difference between an ectotherm and an endotherm?

Ectotherms, including reptiles and amphibians, are organisms that don't possess the ability to generate sufficient heat to keep themselves warm. As such, they are dependent on environmental sources of heat, such as sunlight. This explains why most ectotherms are confined to warmer parts of the world, and why snakes in particular can often be seen basking on roadsides in many countries.

Endotherms, in contrast, do possess the ability to generate their own body heat. Mammals and birds are the only endothermic classes of organisms. Because of this trait, many mammal and bird species have been able to colonise some of the coldest parts of the planet.