Biomes are regions in a Minecraft world with varying geographical features, flora, heights, temperatures, humidity ratings, and sky and foliage colors - gamepedia.com 
A river bisecting a jungle biome. At the top right is a forest - gamepedia.com
Biomes are climatically and geographically defined as contiguous areas with similar climatic conditions on the Earth, such as communities of plants, animals, soil organisms, and viruses and are often referred to as ecosystems.
Biomes separate every generated world into different environments, paralleling the real world; examples of biomes include the forest, jungle, desert and ice plains - wikipedia
A river running through a mesa biome, with a savanna biome in the bottom right - gamepedia.com
Biomes are split into 5 categories based on their temperature:
- snow-covered
- cold
- medium
- dry/warm
- neutral
This prevents biomes with huge temperature differences being placed side-by-side. Examples of Minecraft biomes inluce the Ice Plains Spikes, Flower Forest and Taiga M.
There are 61 distinct biomes which can be categorised into the following groups:
- Snowy biomes
- Cold biomes
- Medium/Lush biomes
- Dry/Warm biomes
- Neutral biomes
- Unused biomes
Biomes can be distinguished by the grass and leaf colors in the biome, along with the types of blocks present (e.g. types of trees or other plants like cacti, sand coverage in deserts). Biomes are pseudo-randomly generated using the Map Seed.