DVD o-ring packaging is a kind of packaging seen on some DVDs sold in retail stores. Other more common terms for the packaging are sleepsleeve or slipcase.
An o-ring package is usually a cardboard or metal sleeve that goes over the plastic DVD case. Many times they are decorative cases that have different artwork than the main case they are covering. An o-ring package may have the film's original poster art on it, while the case itself might have different art. For example, sometimes an o-ring case will be used to differentiate between a special edition of a DVD and a standard edition.
O-ring casing is not specific to DVDs. There are CDs, video games and Blu-rays that ship with o-ring cases over the main plastic case. Just like with DVDs, they are typically more common on special or limited editions than on regular releases.
O-ring cases serve no real function aside from being decorative. Some retailers and wholesalers see them as a hindrance instead of an asset because they make shelving the DVD more difficult. Many times an o-ring case is just a little too big to fit on standard DVD shelves. Some movie studios offer both o-ring and regular versions of DVDs to retail stores who do not like the special o-ring cases.