What is meant by a movie opening and how are movie openings defined?

A movie opening is the introduction to a film, typically lasting a few minutes. After a film introduction, there will be often be opening credits, signifying that the main story is about to begin.

The purpose of a movie opening is to immediately interest the audience that are watching the film. Movie openings also serve to give the audience a taste of what is to come within the film, and what they can expect to see. 

However, they are very different to theatrical/teaser trailers. Trailers like this are designed to show people interesting/informative moments from the movie, to get people to go and watch it. A film opening's sole purpose is to grab the attention of people watching, whilst also being relevant to the overall plot. Film openings will typically establish characters and plot within it's sequence. 

What conventions do movie openings share? 

Movie openings will usually share similar conventions. Often, a movie opening will feature a flashback to show a certain characters situation before the events of the film. A film opening will often start with an establishing shot to show the audience the environment in which the film is set, and also to clarify mood/genre of the film. For example the establishing shot of a horror movie may be that of a huge mansion, surrounded by tree's and seemingly in the middle of nowhere, while rain pours outside and thunder can be heard in the distance. An establishing shot of a romance film may be that of a couple holding hands, walking slowly away from the camera with the Eiffel Tower in the background. These are examples that can show what importance an establishing shot has over perceived genre of the film. These examples also show that genres can each have their own specific conventions for their film openings, for example spooky sound effects for a horror movie and stunning visual scenery for a romance. 

There are also a lot of films that will start with a chase scene or a some sort of scene with a dramatic nature. This serves to immediately interest the audience.

Finally, technology has had a big impact on film openings in recent years. For example if you look back at a classic Alfred Hitchcock movie, the movie will probably have a gentle opening with not much going on. Films these days (for example Quantum of Solace) will often begin with huge set pieces as technology has advanced a lot.