Is there a name for it? Sometimes in films we see most of the body of the main characters talking except maybe the legs. I am wondering if there's a particular word to describe these movie "shots" if we can call them that.
Yes, this is called either the "Medium Wide Shot", the "Cowboy Shot", or the "Medium shot", depending on how much of the legs are shown.. As James K mentions, these are jargon, and not in general use by everyday English speakers -- meaning the average person would have no idea what you mean.
More info for you: The Ultimate Guide to Camera Shots (over 50+ Types of Shots and Angles in Film). See Section 1 for the names of various shot sizes.