pollution mean the presence of undesirable and harmful things in air water etc.

pollution of of different types:air pollution , water pollution, thermal pollution  and , land pollution.

air pollution:the harmful gases present in the air causes air pollution.

water pollution:the undesirable things that are thrown into the water causes water pollution.

thermal pollution:the increase of temperature of the water in water bodies due to the hot water released from the factories causes thermal pollution.

land pollution:the wastes thrown on land causes land pollution.