An ectotherm is an organism who’s internal sources of heat are of small importance in controlling its body heat. Rather, these organisms rely on environmental heat sources. Ectotherms usually live in environments that are typically constant in temperature where they can either bake under the sun or seek shade when necessary. During periods of cold weather, some ectotherms enter a state of torpor where their metabollism slows or completely stops.
Some examples of ectotherms are: frogs (like the one in the picture), snakes, turtles, butterflies, and many other reptiles and amphibians.