A heist is, simply stated, a coordinated robbery of an institution, home, or other secure place. A heist generally involves more than one person coordinating to steal something valuable, though one person can commit a heist. This act is theft, and it is illegal just about everywhere in the world. In the media, the word heist has come to mean a coordinated robbery, and it has been glorified in film and television as an adventurous, if dangerous, experience.
The word heist most likely comes from the word hoist, which basically means to lift. It is an American slang term that originated in the 1920s and came to mean someone who would steal, or lift, property from a store or other institution. While it is not an official term for robbery in terms of law, it has come to mean any theft that involves robbery and planning for robbery. It is also sometimes called a caper, and today a heist generally refers explicitly to a story or film about theft or robbery rather than a real act of robbery.
In film, a heist takes place in three parts. The first part of the film focuses on the gathering of the thieves, touching on their backgrounds and the circumstances of their criminality. Once the thieves are assembled, they begin to hatch a plot to steal something, usually something notoriously valuable. It is during this part of the film that the viewer is steered toward either sympathizing with the thieves or criminalizing them.
In the second part, the heist takes place. It may go according to plan, but more often than not, the caper hits a snag and a plot complication ensues. Many times there is an enemy to overcome; perhaps a rival group of thieves, or most commonly, a sly police detective who is on to the gang. Once the actual caper has taken place, the third part of the film begins, in which the plot begins to resolve itself and the viewers get to see the fate of the criminals.
In the past, it was not uncommon to see the criminals get caught and justice served for the crime. Today, however, many films portray the criminals as the heroes, and the institution being robbed as corrupt institutions worthy of being swindled. Such a set up depends largely on the mood of society at any given point in history, and current events play a large role in deciding whether the criminals will be successful or not.