What is NEAT (non-exercise activity thermogenesis)?

In one line

NEAT is the energy the body uses for everyday movement such as walking, standing and housework, leaving out sleeping, eating and exercise.

What is NEAT (non-exercise activity thermogenesis)?
The calories you burn outside of workouts
Diet talk often says "raise your NEAT." It refers to the calories you burn moving around during the rest of the day, outside your hour at the gym. What exactly does it include?
In short
Energy used by everyday movement that isn't exercise
NEAT is the energy the body uses for all daily activity except sleeping, eating and exercise. Walking to work, typing, housework, yard work, even fidgeting with your hands and feet all count.
What the name means
"Heat made by activity that isn't exercise"
NEAT stands for Non-Exercise Activity Thermogenesis. "Thermogenesis" means the body making heat. When the body uses energy, much of it comes out as heat, so the energy used by moving is described with the word "heat."
How it differs from exercise
Whether you do it on purpose for fitness
Exercise is physical activity done on purpose, usually regularly, to improve fitness or health. Gym workouts and running are exercise. NEAT is the energy used by movement that is just part of daily life, without that purpose.
Its place in the day's total
Splitting the "activity" part of TDEE
The energy you use in a day (TDEE) splits into basal metabolic rate, the energy used even at rest; the energy used to digest food; and the energy used for activity. The activity part splits again into exercise and NEAT. Most of the energy a person uses beyond resting comes from NEAT.
How it is measured
Subtract the rest, or add up each activity
There are two ways to measure NEAT. One is to measure the whole day's energy use and subtract basal metabolic rate and the energy used for digestion. The other is to measure the energy used by each activity, such as walking or standing, and add them up.
Small movements add up
Even fidgeting in a chair
In an experiment that compared activities with lying at rest, just standing still used a little more energy. Fidgeting with your hands and feet while sitting used about 1.5 times as much. Countless small movements like these, added up over a day, make up a person's NEAT.
It varies a lot between people
Your job and lifestyle change your NEAT
NEAT varies a lot from person to person. People who do physical work such as farming have high NEAT, and NEAT falls as life gets more convenient and industrialized. Depending on body weight and how active a person is, NEAT reaches up to about 2,000 kcal a day on top of basal metabolic rate.
It changes with how much you eat
Up when you eat more, down when you eat less
NEAT is not a fixed number. In experiments, NEAT went up when people ate more and went down when they ate less. That is why NEAT is seen as an important part of how body weight stays the same or changes.
Common myth
Does everyone gain the same from eating the same extra amount?
No. In an experiment where people without obesity ate the same extra amount every day, the fat they stored differed by up to 10 times from person to person. This difference was explained by how much NEAT rose. The more someone's everyday movement increased after overeating, the less fat they stored.
Summary
Movement outside workouts makes a big difference
NEAT is the energy used by everyday movement other than sleeping, eating and exercise; it differs a lot between people and changes with how much you eat. Even when people ate the same extra amount, how much their NEAT rose changed how much fat they stored. Related terms: TDEE, basal metabolic rate, calorie surplus.