or
Whichever came first.
I know there are thoughts about ballgowns being too similar to Royal, Prom and wedding gowns, but that isn’t true actually. They are all different: made specific to different events - although similar because they are dresses - and are used for different people.
A Ballgown is indeed a gown for Balls, Galas, masquerades in order to make you, as the VIP, or your partner, who could be the VIP, stand out and gather attention from other companies like the met gala when all the celebrities dress excessively. They look stunning to make themselves known to designers and the world. Ball gowns can also be designed in a more absurd way than any other dress in the world because there is room and money for it. They can be designed with any fabric and if a designer can hold the world record for the longest dress train… they will go for it. Lifted by petticoats. A ball gown can have a thousand fashion themes as long as it meets the requirements of the event.
Yes, the silver dress is a ball gown.
Note: there is the duchess dress shape, also known as the ballgown shape. However, there is the ball gowns as an the type of dress too.
This is a petticoat, btw.
A wedding dress is for weddings. There is this confusion about these dresses because they can have the “duchess shape” sometimes, but a wedding dress is not designed to be a ball gown. Usually, wedding dresses are designed with specific lace details and up to one or two colors. they are most likely to have trains longer than any other dress as well… unless a celebrity at the Met Gala wants to be extra like Cardi. There are designers who will most likely add flowers, pearls or extra sheer fabric so as to not take away from the bridal look. Some people do wear the simpler wedding gowns to proms and balls (and vice verse)… but really that’s not each other’s purpose. We choose them because they are gorgeous, aka specifically designed for brides.
A royal gown is especially not a ball gown. like I mentioned before, there are ball gowns that are specifically designed for galas and such, and there is also the ‘ballgown’ shape. But not all royalty wears a ball gown. A royal gown doesn’t, even need the shape. A royal gown shows the status of the nobility who wears it and is specifically designed in their sovereign favor. Not to be used as a wedding dress. Can be used as a ball gown at royal events.
A Prom dress is for prom. 
That’s it. At a job, a boss would host a prom for their employees. At school, the faculty will host it for their students. You don’t have to dress up as a bride or like a queen unless it’s a costume party and I assure you… even the costumes aren’t as fancy. They are elaborate in their own way and most likely cheaper to get or can even be rented. Some people may actually have the money to get their dress made or lucky to have a seamstress in the family. The dresses can also have the duchess shape but they are not as high lifted - they don’t have petticoats.
A Quinceanera gown is not a ball gown either… but it is a special gown to a 15-or-16-year-old coming of age, birthday-girl bash. It’s a tradition within the Hispanic nation for young girls and it’s a beautiful event. It’s like being at a wedding but it’s a birthday ceremony. Btw, these dresses definitely have petticoats. 
It’s so fun.
This is my case to reopen one of the Ballgown posts because I would really like one of them to get support for it. I adore ball gowns. Plus, they are right, we don’t have any “duchess/ballgown” shaped dresses. The dresses in the episode catalog are A-line, mermaid, short, fit and flare, sheath, asymmetrical, wrapped. But, not a duchess shape, the REEEAAALLLYYY puffy gowns. We don’t have Quinceanera gowns either.
