Zoologically, when something is endothermic, it just means that the creature absorbs heat around them. Humans are a great example of endothermic animals. Our bodies stay roughly about 98.6°F, or 37°C. For our bodily functions to occur normally, our temperature cannot drop below a certain point or raise above a certain point, we will actually die. We are dependent on our own closed, self-regulating heat system. However, for perspective, ectothermic animals such as reptiles are dependent on external energy sources, like heating lamps and the sun, for their bodies to stay functional.
Hope I could help!
