BMR is your basal metabolic rate at complete rest; TDEE is total daily expenditure including everyday movement and training. Nutrition targets always work off TDEE.
BMR only covers what heart, brain and organs burn lying still — for most people 60–70% of daily needs. TDEE adds everyday movement, digestion and training on top. The classic dieting mistake is subtracting your deficit from BMR instead of TDEE, which digs a hole far too deep: you lose strength and muscle and quit after two weeks. Also worth knowing: every formula is an estimate with a margin of roughly ±10%. The honest number is the one you back-calculate from two or three weeks of weight data.