"Temperature" in this case refers to the amount of energy they emit due to hawking radiation. By comparing to a black-body curve, you can define a temperature

"Temperature" in this case refers to the amount of energy they emit due to hawking radiation. By comparing to a black-body curve, you can define a temperature for the hole. Obviously it's not a real object with a real temperature -- if it were, I believe the temperature might be infinite -- but this still works for the purposes of deciding whether it'll grow or shrink.