“Net zero” means that for each ton of greenhouse gas emissions produced, an equivalent amount must be removed from the atmosphere. That would reduce the impact on the Earth’s climate to net zero.
In practice, achieving net zero means combining measures aimed at reducing existing emissions with actions designed to remove carbon dioxide from the atmosphere. The former includes, for example, switching to renewable sources of energy and improving energy efficiency, and the latter includes methods like reforestation as well as carbon sequestration and storage technologies.