Tempering is a technique often used in making custards. To make a sweet custard, eggs are mixed with sugar and then combined with hot milk or cream, and heated just to the boiling point.
To prevent the eggs from curdling or scrambling, first a small amount of hot cream is whisked into the eggs. This raises the temperature of the eggs gradually. This technique is called tempering.
Next, the warmed egg and cream mixture is added into the hot liquid, stirring all the time. The eggs won't curdle at this point, because they have been warmed gently.
Keeping the heat low, stir the mixture until the eggs begin to cook, thickening the custard to the point where it can coat the back of a wooden spoon.