Dumping is a price practice where the price of a product in the importing country is kept less than the price charged at the exporting country. So, under dumping, the exporting country (firm) charges a less price in the foreign market compared to the domestic price.
Dumping is a price strategy adopted by the exporter to capture the foreign market. For example, suppose China is exporting iron and steel to India. When the price of iron and steel charged by the Chinese exporters in India is lower than the price charged in the Chinese market, it will be termed as dumping.
The vicious form of dumping is predatory dumping, where an exporter charges very low price in the foreign market to eliminate competitors.