(a) The phenomenon of spending cold and dry winter season in an inactive or physiological dormant state by an animal is termed as hibernation eg. northern ground squirrels, polar bears, etc. It is also called as winter sleep.
The phenomenon of spending dry - hot period (summer season) in an inactive state by an animal is termed as aestivation e.g. ground squirrels in south - west deserts. It is also called as summer sleep.
(b) An ectotherm is an animal in which the internal body temperature is the same as the temperature of its surroundings e.g. fish, reptiles. Ectotherms cannot control their internal body temperature and therefore have to stay in either the sun to stay warm, or the shade to keep cool.
Endothermic are animals that can maitain a constant internal body temperature, regardless of the temperature of their surroundings e.g. Birds, mammals.