ELI5: Explain Like I'm 5

Saturation vapor density

Saturation vapor density is the amount of water vapor (tiny liquid water droplets) that the air can hold before it can't take any more. It is related to the temperature of the air. When the air is warm, it can hold more water vapor and the saturation vapor density is higher. When the air is cold, it can't hold as much water vapor and the saturation vapor density is lower.