The nitrogen (N) that we use as fertilizers and industrial materials, as well as the reactive N generated during fuel combustion, eventually leaks into the environment in the form of dinitrogen (N₂) or reactive N. Human-induced N loss to the environment is collectively called N waste. This is the same idea as what is generated after using various resources and is called waste. However, N waste is a concept proposed around 2020, and its definition is still controversial.

N waste is broadly divided into two types; N loss to the environment during production without reaching the final product, and N loss to the environment accompanied with consumption of the final product. An example of the former is N that is not absorbed by crops but is released into the atmosphere or water via soil from input N fertilizers. An example of the latter is N as excretion after food consumption. When N waste lost to the environment as reactive N, it causes various types of N pollution. Although gas and water treatment partly convert reactive N in exhaust gas and wastewater back into harmless N₂, the operation of treatment facilities also require resources and costs. It is important to take measures to reduce the original amount of N waste.