If I said the word "Extra", most likely you would think something or someone that is not essential to the original such as supersizing your fast food order. Or you might buy something because of all the other things included to make the deal seem sweeter.
If your mind works a different way, you might have thought of the people you see in television shows and movies. The people who walk by in the background, the ones who sit in all the other tables in the restaurant, or the people who fill out the movie theater. They make the scene seem natural yet they do not say a single word because they job is to make it all a reality.
You might even think of the dancers who dance behind the stars on a video, movie, or show. The ones who mirror the vocalist's movements turning it into something more. Even in movies, dancers are hired to complete a ballroom, or perhaps are the other students in a show like Glee or Fame. They turn a few people into a fully populated ball complete with those who sit watching and those who dance.
If a music video or movie wants better than average looking people, they might hire models who specialize in music videos or short films from an appropriate agency. Even people on those exercise videos often hire extras to exercise with them. The ones who are behind the leader, who exercise with them and provide the modifications if you need something a bit easier or the higher level than the leader.
Of course, we mustn't forget the political arena because politicians are known for hiring people to fill out crowds and make it look as if people support this particular candidate. Even Trump admitted to paying a company to hire people for one of his rallies. Apparently, politicians do this often enough to warrant the existence of several companies who provide the extras.
Are you throwing a Murder Mystery Party at your house, or for an event, you can hire everyone you need for the party and each person who is hired, is considered and extra because you hired them for a short period of time. In addition, there is a whole class of workers classified as extras because they fill out personnel for an event or job.
If you hire a caterer who provides the food and staff for an event, the waiters and waitresses, the cooks, the cleaning staff, everyone. They are all extras, people who are hired to be there, to provide services in the background, much like extra's in movies and political rallies.
There are extras everywhere you look in this world. I'm sure there are other types of extras in places I've not thought of. I hope you enjoyed this. Please let me know what you think, I'd love to hear. Have a great day.