The subject is related to carbon footprint.
Being carbon neutral refers to achieving a net carbon emission of zero by balancing a measured amount of carbon released with an equivalent amount removed. An example is to plant trees that remove CO2 from the atmosphere where it would otherwise function as a greenhouse gas and contribute to global warming. In this way an individual can compensate for emissions caused by the use of fossil fuels.
Carbon neutrality can also by achieved by emission trading. Here an individual or a company can invest in carbon credits that guarantee that an amount of carbon emission corresponding to the credit has been saved elsewhere. More precisely, the seller of the credit has not used all of their carbon quota so some of the buyers emission is being offset by what is not emitted by the seller. This brings the overall emission down in the most cost effective way.
The carbon neutral concept may also include other greenhouse gases. In such cases these other greenhouse gases are measured in terms of their carbon dioxide equivalence. In this way it is easy to compare the effect of the emission of different greenhouse gases.
Carbon neutral is also sometimes called climate neutral.