Apparent temperature is the temperature equivalent perceived by humans, caused by the combined effects of air temperature, relative humidity and wind speed. This is an arbitary figure as everyone perceives temperatures in a different manner due their personal tolerance to heat and cold. It does however provide a comparison that allows you to work out what clothing/sun protection you may need.
Quite often the real temperature and the apparent temperature can be very different.
This image from the Australian Weather Bureau shows the actual temperature at -7.2° Celsius with the apparent temperature at -10.1° Celsius in Canberra on the morning of 2 July 2017. As you can see from the image, there was no wind but 94% humidity