Dew point
The temperature at which air becomes saturated and moisture starts to condense into water.
The dew point is the temperature at which the air can no longer hold all its moisture, so water condenses out — onto grass as dew, or onto a cold window, pipe, or wall inside your home. Unlike relative humidity, dew point is an absolute measure of how much moisture is actually in the air, so it's a better gauge of how 'muggy' it feels. When a surface in your house is colder than the dew point of the surrounding air, you get condensation — the root cause of foggy windows and hidden moisture inside walls.