TDEE (Total Daily Energy Expenditure) is the total calories your body burns in a day including exercise. Eating at TDEE maintains weight, below it loses weight, above it gains weight.
BMR is calories at complete rest. TDEE multiplies BMR by an activity factor to account for daily movement. Most people's TDEE is 1.4–1.9× their BMR.
Eating 500 calories below TDEE creates a deficit of 3,500 calories per week — approximately 0.5kg (1lb) of fat loss per week, considered a safe sustainable rate.