The terms warm-blooded and cold-blooded are a bit inconsistent to the actual meaning of these words.
Cold-blooded animals are the animals that are incapable of regulating their body’s temperature with respect to their surroundings while warm-blooded animals are able to maintain their body temperature irrespective to their surroundings. Reptiles, insects, fishes, amphibians and other invertebrates are cold-blooded, while mammals and birds are warm-blooded.
Before I go any further, I want to discuss some terms related to thermo regulation:
Endothermy and Ectothermy
Thermoregulation in animals are mainly classified into two categories endothermy and ectothermy. Endothermic animals are the animals that create most of their body heat through various metabolic processes inside their body. While ectotherms are those animals where the metabolic processes do not produce the sufficient amount of heat to maintain their body temperature. They use external sources to maintain their body temperature.
Homeothermy and Poikilothermy
Homeotherms are the animals that have a constant body temperature while Poikilotherms do not.
Now to clear the air, an animal is referred to as warm-blooded if it is an endothermic-homeotherm, while ectothermic-poikilotherms are referred to as cold-blooded animals.
The endotherms have larger number of mitochondria per cell in comparison to ectotherms, which enables them to generate more heat by metabolization of sugars and fats. Ectotherms have their own way of regulating temperature, they often use their surroundings to maintain their body temperature. For ex. Fishes move from colder to warmer water when required. The dependence on surrounding, makes it harder for ectotherms to survive in harsh climate. Endotherms have their own problems as well, to maintain their body temperature they have to provide for the source of energy, i.e. food. So, they have to eat at regular intervals, while ectotherms are able to survive without food for longer periods of time. As, the metabolism is lower in ectotherms, they usually have lower speeds, as compared to endotherms.