What I mean when I say…
Basal metabolic rate
How much energy your body needs just to function each day without taking into account exercise or general movement.
Calories
kilocalories (kj or kcal on labels), these are units of energy in the food we eat, and our bodies burn for fuel.
Calorie deficit
Consuming less energy than your body needs.
Example: If you need 2500 calories a day to run your body and maintain weight, you may decide to eat 2000 calories a day instead, which creates a 500 calorie deficit per day. Your body still needs those 500 calories so it takes them from your fat stores instead of the food you eat, resulting in fat loss.
Metabolism
How your body burns food/fuel/energy/calories (these four terms are inter-changeable, they all mean the same thing) in your day to day living and activity.
Thermic effect of food
How much energy it takes for your body to digest, absorb and use the food you eat.
Thermogenesis
Increased production of heat in your body after eating food as it processes nutrients.