During the process of respiration, gases like oxygen are ingested and chemically broken down, or oxidized, to provide energy for the living organism. This process ends with the expulsion of a different gas or byproduct once the process is complete. For humans, oxygen is inhaled through the lungs and broken down as carbon dioxide is exhaled, while with plants, the opposite occurs, and carbon dioxide is ingested and oxygen is produced instead.
There is an important distinction between plants that absorb carbon dioxide and animals that inhale it. For plants, their process is referred to as cellular respiration while respiration that solely inhales oxygen and emits carbon dioxide is simply referred to as respiration. This process happens for all kinds of living creatures. Mammals experience it in the lungs, fish experience it in the gills, earthworms experience it in their skin and amoebas experience it in their cell surface.
There are two types of respiration. The first one is called aerobic respiration. This is when food is broken down to provide energy to the living organism, although it shouldn't be confused with digestion. Aerobic respiration creates ATP, a source of energy, from the breakdown of glucose and creates carbon dioxide. During anaerobic respiration, glucose is broken down as well, except besides energy, lactic acid or ethanol are released, too.