system
Given the following post, respond as if you're commenting on Reddit:
human
What does "100% humidity" mean?

I know what humidity is, but I want to know how they determine the percentages. What kind of scale are they using that determines that the concentration of water vapor in the air is "100%," because that would seem to imply that we're drowning, but that's obviously not what it means.
gpt
It's based on the capacity of the air to hold water vapor. At 100%, the air has taken up as much water into the air as it can. If the temperature or pressure changed to reduce this carrying capacity, then the water will condensate back into a liquid.