Video interpolation or Motion Smoothing, sometimes called the 'Soap Opera Effect', is a feature on modern flat panel TV's meant to combat motion blur. This feature works great for sports programs, keeping everything crisp and clear so you can keep track of the game, but many big names in the Film industry are starting to speak out against it.
Motion Smoothing works by generating extra frames of footage between existing frames to make the image appear more fluid. In theory the feature is supposed to make everything crisper, clearer, and give the illusion of a higher frame rate. However this feature does change the way you perceive content, and can create situations where you aren't getting to experience movies the way the creators intended. The feature is usually turned on by default and difficult to disable.
Just this week, Tom Cruise and director Christopher McQuarrie put out a short PSA about Motion Smoothing, and how it's inadvertently changing an artists intended vision. While it looks great for sporting events, the extra frames generated can make movies look a little... weird at times. Depending on the brand of your TV, menu settings will vary. Whether it's called motion smoothing or motion plus, the setting can usually be found in the screen display or picture settings.