What is the difference between a quiche and a tart?

During the last few weeks, I was wanting to make things for lunch and I decided that a quiche would be a good idea. When looking for recipes I also found a prosciutto and feta tart which was remarkably like a quiche. I began to wonder what the difference between a quiche and tart was and whether it was just a name or was there a difference in technique.
The quiche and the tart I made were similar with only a few differences in the ingredients. I decided to investigate this further and maybe someone else out there has the same question.

To begin with, a tart can be either sweet or savoury however sweet tends to be more common. A quiche is always savoury consisting of an egg custard filling.

Further looking around the internet led me to Joe Pastry who states that tarts have two possible origins. The first being that it was a layered item of food and the second that it came about after the popularity of pies, removing the top pastry and showing off more filling. Does this mean that a quiche is more of a liquid start and a tart has a more solid filling? Going over many quiche recipes a desired ratio of egg and milk/cream or other dairy does not seem to appear. However, in quiches, the egg and milk/cream ingredients are higher in proportion than the fillings of tarts or flans. If other ingredients are the star, then it is a tart. All else fails a quiche is a savoury tart, so everything is a tart.

I thought that further clarification may come from food history but that brought up more questions.

Did you know that the quiche is thought to have dated back to the 16th Century? The classic Quiche Lorraine was created in Nancy, the second largest city in Lorraine, France. However, there are also beliefs that the quiche was created in Germany and later enhanced by the French. It is likely that quiche is German as the name derives from the German word kuoche meaning cake, and Kueche in Franconian. Lorraine was also a part of the Lotharingia Kingdom and was not part of France until 1737.

Due to the proximity of Lorraine to Germany and changing rulers between the two countries over history, it is possible that the true origin may not be determined. Many food items from the past may have been made in various places and then enhanced due to cultural changes. Ending up as the item we know now.

The egg mixture of custard, more commonly known as an English dish are reported as served at banquets of Henry IV in the 1300’s. Rather than just the small custard tarts that we know today Queen Elizabeth I was thought to love the tarts so much that especially large tarts were created for her and her parties.
There is also the Portuguese egg tart named Pasteis de Nata which were created in the 13th Century by monks. However, it was believed that the monks learned of the tarts when they were based in France to use up egg yolks.

Hong Kong have their own version of the custard tarts. The pastry shell is made differently however the British introduced these to China in the 1920s.

There are many variations of egg fillings with a pastry shell and we can call them European if we wish. Ultimately, does it matter where they come from? What really matters now is who makes the best version.
To figure this out I have some baking to do.