Principal photography is the phase of film production in which the bulk of the movie is filmed, with actors on set and cameras rolling, as distinct from pre-production and post-production. Principal photography is typically the most expensive phase of film production, due to actor, director, and set crew salaries, as well as the costs of certain shots, props, and on-set special effects.
While it is common for a film to lose its greenlight status during pre-production - for example, when an essential cast member drops out or unexpectedly dies, or some scandal engulfs the studio or an actor - it is rare for the film to lose financing once principal photography has begun.
Feature films usually have insurance in place by the time principal photography begins. The death of a bankable star before completing all planned takes or the loss of sets or footage can render a film impossible to complete as planned. For example, sets are notoriously flammable. Furthermore, professional-quality movie cameras are usually rented as needed, and most camera houses do not allow rentals of their equipment without proof of insurance.
Once a film concludes principal photography, it is said to have wrapped, and a wrap party may be organized to celebrate. During post-production, it may become apparent that some shots or sequences are missing or incomplete and are required to complete the film, or that a particular scene is not playing as expected, or that a performer needs to be replaced entirely. In these circumstances, additional material may have to be shot.
If the material has already been shot once or is substantial, this process is referred to as a re-shoot. However, if the material is new and relatively minor, it is often referred to as a pick-up.