Non-Exercise Activity Thermogenesis, or NEAT, is anything you do that requires energy beyond focused exercise and your Baseline Metabolic Rate (BMR). Your BMR is the energy (calories) you burn just existing/breathing. If weight loss is your goal, you should follow the formula: Calories ingested < BMR+Exercise+NEAT = Weight Loss (obviously, it's a little more complicated than this formula, but this is a big part of it!)
NEAT is a simple and important way to increase this calorie deficit. NEAT can be as simple as standing up straight, or as intense as doing jumping jacks during commercial breaks or credits. NEAT can be as deliberate as taking a walk for a couple of minutes for every hour that you sit, or as discrete as Kegels or isometrics at a red light. Anything extra will add up! Over the course of a day, you could burn 250 extra calories with these additional activities. Plus about 250 from a basic work out, and that's 500 calories added to your BMR deficit! The key is to find what works for you.
Will you take the stairs? Will you park farther away? Will you meet up with a friend for a walk instead of a meal or drinks? Will you take a walk on your break? Will you do some calf raises while you wait in line? The options for increasing your NEAT is actually limitless. You just have to be aware and actively make the change.