Bottle Episodes: Great Story on a Low Budget.

A bottle episode is an episode made using as few cast members, sets, and effects as possible. The stories are usually set in only one location. Due to the lack of location the episode is often used as a chance to develop characters and reveal more about them. In television this is very important as character development happens over a much longer time and to a much smaller degree. Very often characters will not have major changes to who they are. For one example, we look to The Office. At the start of the show Michael Scott is an endearing idiot and by his departure his is just as much one as when he started. Sure Michael learns some lessons but none that change his overall character. Bottle Episodes aren't trying to break this form, they simply offer a chance for more depth of the characters to be revealed. Breaking Bad and Community both have good examples of bottle episodes.

Yeah bitch, bottle episode.

In the Breaking Bad episode Fly, Walt and Jesse must kill a fly lose in the superlab to save them from contaminating a batch of blue sky. Walt and Jesse are the only major players to appear on screen and the episode is set almost entirely in the superlab. The lack of location change and action forces the characters to deal with and confront the consequences and emotional weight of Jesse's girlfriends death. This isolation would not have been doable in a regular episode, or at least have the same effect.

Six Seasons and a Movie

The cancelled too soon meta comedy Community also did a bottle episode, one that is often considered the series best episode. The episode takes place entirely in the Greendale Library and uses only the main cast. Community uses this episode to reveal more secrets and backstories about the Greendale Seven. At the start of the episode Abed even points out that their situation is shaping up to be a bottle episode. While originally acting civilized, the episode shows what happens as time stretches on and what they really think about each other comes to fruition. 

The idea of a bottle can appear in movies though it is often done for more of an artistic reason rather than a budgetary one. The films tend to focus more on human nature, similar to what Community does in it's bottle episode, One very simplistic example of this is a film called Buried. In the film, Ryan Reynolds finds himself buried alive. He is the only character to appear on screen the entire film and there is never an exterior shot. Every shot takes place inside the coffin and the same shot is never repeated. 

In television, the bottle episode style of filming is a great way to develop character and keep the budget low.