Permanent ventilation is the ventilation that you never close for any reason -- open 24/7/365.
This ventilation is best installed above the chickens' heads while they're sitting on their roost so that there are no drafts no matter how windy. This photo is from an article on cow barns, but the same principle holds.
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Windows that are closed in the winter, the pop door, and anything else that you close up sometimes and have open other times are supplemental ventilation. They don't count towards that 1 square foot per hen.
Some people use fans to improve the airflow in their coop but this has to be done with care because installing an ordinary household fan where the motor will be exposed to the dust from feathers and bedding carries a significant risk of fire.
There are fans specifically made for outdoor and/or barn use that are sealed to reduce this risk.