The energy spent above the normal resting metabolism rate due to the cost of processing food during digestion.[1]
When you eat, your body responds to this by increasing the rate at which you expend energy or calories and this is called the Thermic Effect or meal induced thermo-genesis. How much energy your body spends is based upon what the food is (it's nutrients and structure). This energy is spent on digestion of food, metabolism of food, conversion and storage of macronutrients.
Gibney et. al. (2002) states that the thermic effect of food represents about 10% of the caloric content of the meal that is consumed.[2] However, McArdle et. al. (1986) points out that it can actually vary "from 10 - 35% of the ingested food energy in normal individuals depending on both the quantity and type of food eaten."[3]