Plain English Meaning
Two numbers shown side by side: how warm the air is right now, and how cool it would have to get before moisture starts forming. When the two numbers are close, the air is nearly ready to produce fog or low clouds.
Full Definition
A paired weather value showing the current air temperature and the dewpoint temperature at a given location. Temperature is the actual temperature of the air. Dewpoint is the temperature to which that air must be cooled, at constant pressure, for it to become saturated and produce condensation (visible moisture such as dew, fog, or cloud). The two values are usually reported together because the gap between them indicates how close the air is to saturation.