Legally DVD grant you the right to private performances. So if you get a group of friends together to watch a movie, that is fine. If you own a bar that has TV’s and a DVD player and play the movie there, its illegal.
mpaa.org/contentprotection/public-performance-law
"No additional license is required to privately view a movie or other copyrighted work with a few friends and family or in certain narrowly defined face-to-face teaching activities. However, bars, restaurants, private clubs, prisons, lodges, factories, summer camps, public libraries, daycare facilities, parks and recreation departments, churches and non-classroom use at schools and universities are all examples of situations where a public performance license must be obtained. "
Copyright laws view the purchasing of such files, DVDs and the like not merely as purchasing their official copy, but purchasing a certain type of license for how you are to use that copy. This is where we get into the concept of intellectual property. You’re not purchasing the movie, you’re purchasing the limited license to the movie and receiving the movie in a certain format.
This is why it is considered illegal to make copies and distrubte them. You did not purchase the movie or the song, you purchased a license to a movie or song which gives you a right to one official copy and the right to make copies (like back ups) for your private use.