BMR (basal metabolic rate)
BMR is the energy your body uses at complete rest to keep basic functions running. In practice almost nobody measures it directly; the figures you see are estimates from a prediction equation fitted to a study population.
Example
Mifflin-St Jeor for an 80 kg, 180 cm, 30-year-old man gives 1780 kcal/day. A woman of the same size and age gives 1614 kcal/day.