This is the amount of heat needed to raise the temperature of an object by one degree Celsius. It's like how much food (calories) it takes to gain one pound on your diet.
This is a type of reaction that absorbs heat from its surroundings. Imagine if eating celery actually burned more calories than it gave you - that's an endothermic reaction!
This is a type of reaction that releases heat into its surroundings. Like when you eat something high in sugar and feel a sudden burst of energy, an exothermic reaction gives off energy too!