Carbon. Element #6 on the periodic table. 18.5% of the mass in a typical human body, second only to oxygen. You'll find it in coal, gasoline, natural gas, but also food, fermented beverages, the frame of my now-obsolete road bicycle...and the atmosphere, again with its pal oxygen in the form of carbon dioxide.
Guelph has a goal to be a Net Zero Carbon community by 2050, but that doesn't mean we're getting rid of booze, carbon-fibre bicycles, or a significant portion of our bodies. The target refers to emissions of greenhouse gases (GHGs), the culprits behind climate change.
Carbon dioxide is the one we talk about the most, but other gases play a role. Human contributions to our global GHG inventory also come from methane, nitrous oxide, and ozone. So when we consider these other gases, we compare their climate change impact to that of carbon dioxide, and measure that in "tonnes of carbon dioxide equivalent", or tCO2e.
When we're talking about climate change, net zero carbon means net zero GHG emissions.
Then there's that loaded word, "net". Think of "net income" on your tax return: the income after removing any deductions, like the basic personal deduction, charitable contributions, and a (precious) few other items. If your deductions bring your net income to zero, you don't pay any tax. In the same way, when we're talking about GHG emissions, "net" means what's left over once we consider items that actually serve to reduce carbon. This would include: