A biome or phytogeographic zone is a community of organisms, plants (flora) and animals (fauna) that inhabit a certain region of planet Earth, with its own climatic characteristics.

Biomes do not have a clearly defined border. Rather, one biome gradually blends into another. The areas between biomes are called ecotones. For example, shorelines are ecotonic regions because they lie between an ocean biome and a terrestrial biome.

Biomes exist throughout the globe and they differ from one another, mainly because of their physiognomy or visual characteristics, climatic conditions and especially their vegetation. The latter is an essential component of biomes, since the consumers and decomposers that inhabit them depend on it.

In each biome the type of top vegetation (grasses, conifers, deciduous trees) is uniform, but a particular plant species may be different in different parts of the biome. The type of culminating vegetation depends on the physical environment, and this and that determine the type of animals present.

The biome definition includes not only the dominant community of the region, which has reached a high level of stability in its interactions with the environment; but also includes the intermediate communities that precede it, and which are still unstable from the point of view of their interaction with the environment.

The different biomes are divided into three types: terrestrial biomes, freshwater biomes, and marine biomes. Terrestrial biomes are the most varied, and marine biomes contain much more dissolved salts than freshwater biomes.

Terrestrial biomes are distributed, albeit more or less irregularly, like belts around the world. In this way, if a person observes its distribution from the Equator to the North Pole, they find tropical rain forests, tropical savannahs, deserts, temperate grasslands, chaparral, deciduous forests, coniferous forests and ends up in the biome of the tundra in northern Canada and Alaska.

Freshwater (freshwater) biomes can be divided into two types; still or lentic water biome, such as lakes and lagoons; and biome of flowing or lotic waters, such as the waters of rivers and streams. The marine biomes characterized by the oceans, can be found two varieties; the littoral or neritic biome, and the oceanic or pelagic biome.