Question

what are weed ?How are they removed by farmers?

Answer 1

The unwanted plants that grow along with the useful plants in the cultivated field. For example xanthium, parthenium etc. They compete for food, space and light. They take up nutrients and reduce the growth of crop.
Farmers remove it by using pesticides which includes insecticides and fungicides.

Answer 2

Weed is a wild plant which appears where it is not needed.  

At the same time weed also gives competition to the food plants and inhibits the growth of cultivated plants.  Less production of cultivated plants affects the economy, the environment, human health, and amenity.  

They can be removed with the help of herbicides. Herbicides can be defined as the substance which is toxic to weed plants therefore, these chemical substances are used to destroy unnecessary plants.