Net Zero refers to a house or building that generates as much energy as it consumes.On the HERS scale that equates to a 0. If a house was to produce more that it uses it would identified with a negative number.
This can be a gray area as some consider energy as just the electricity used, while others will count all forms of energy used like oil, gas, propane, and electricity. There is another group that calculates it based as how much source energy was used (for example due to line losses, etc… .
In general, most people & programs consider all forms of energy used (point use not source)