Deforestation means
(a) planting more trees
(b) designing a forest
(c) demanding a forest
(d) clearing the forest and using that land for other purposes

Hint: Deforestation has been a major cause of biodiversity loss. It is done by various people due to various reasons- agriculture, cultivation, etc. It results in a fewer number of trees leading to a loss in oxygen gas for breathing.

Complete answer:
It is the conversion of heavily forested areas to barren land or almost barren land. It is done for various reasons such as building a city, for cultivation{jhum cultivation}. Trees are also cut for the wood, they are cut for the various benefits they provide. Therefore, deforestation is cutting off the trees to clear out the land, for various reasons.

Additional Information: 1. Deforestation can result in an increase in carbon dioxide present in the atmosphere, as a lot of carbon dioxide is involved in the biological phenomena which trees take part in. Therefore, cutting down the trees can severely affect the earth's stability.
2. The trees are a huge deal for animals, micro animals, and a lot of different other small plants that depend upon the big trees for shelter and growth, hence cutting down trees may result in habitat loss and fragmentation.

So, the correct answer is ‘clearing the forest and using that land for other purposes’.

Note: Jhum cultivation also known as the wasteful method of cultivation is a major source of deforestation, it is also known as the slash and burn method. In this way, farmers cut down the trees and burn them till the tree becomes ashes. The ash left is used as a biochemical fertilizer to grow more crops and later for grazing the animals. the land is left barren for years as the farmer leaves it and moves to the next land.