Non-exercise activity thermogenesis (NEAT): energy expended for everything that is not sleeping, eating or sports-like exerciseWikipedia
Here’s the fascinating part: NEAT increases or decreases based on how much a person eats.
Physiological studies demonstrate, intriguingly, that NEAT is modulated with changes in energy balance; NEAT increases with overfeeding and decreases with underfeeding. Thus, NEAT could be a critical component in how we maintain our body weight and/or develop obesity or lose weight.Source
So if you over-eat one day, then afterwards you may naturally be more likely to fidget, or wiggle your feet, or walk across the room to throw away the wrapper that normally you’d be too lazy to care about.
Supposedly this explains why some people have no trouble staying lean; their NEAT meter is extra finely tuned. They move more without thinking about it.