A movie is an electronic signal of moving graphics, pictures, or text used to combine a steady stream of images used for entertainment, education, or other uses. This term is often used to describe content that is longer than ten minutes or something you would watch on your TV or at the theater. Whereas video is used to describe short clips or files on the Internet, see the video definition for further information and online example.
To play a movie file on your computer you must have a movie player program that supports the video file you're trying to play. For example, movie players that work with Windows are Windows Media Player (included with Windows) and VLC (that also works on other platforms).