Rain forests were a lush biome, which existed in the game prior to the Adventure Update. They can be viewed as a forerunner to the Jungle biome seen in later versions of Minecraft, due to their denser-than-average vegetation, higher tree concentration and more common large trees. they usually consist of low flat plains and high cliffs and hills but can be mountainous.
Rainforests are wet biomes with many trees, which have a 1 in 3 chance of being large trees, instead of 1 in 10 like all other biomes. They are similar to forests but have a large amount of tall grass and ferns and lush green grass due to temperature and rainfall requirements. A biome is classified as a rainforest if the temperature is greater than 97% and the rainfall is more than 90%. As a result of this, the rainforest can often contain a lot of cliffs and hills because the world generator reduces height variation at lower rainfall values and vice versa.