Tart tin, flan tin and quiche tin..
I think this is one of those Red Queen Things. It is whatever you say it is.
Traditional quiches are deeper than tarts so that could be a difference and either can have a removable bottom so that the finished quiche/tart can be removed for easier slicing.
But I have some with and without removable bottoms. I'm grateful for the solid ones because sometimes the things I'm baking are pretty runny and I'm not thrilled about them leaking all over the place.
Flan is problem because it means different things to different people.
To some, it's a custard that is completely liquid before baking and similar to a creme caramel. I bake mine in a deep dish and turn it out onto a platter.
But I have a flan pan that was clearly labeled as such that is like a tart tin, with a non-removable bottom that is indented. It makes a layer similar to those spongecake "shortcake" shells sold in supermarkets. It's intended to hold a pile of fruit filling.
I can't imagine cooking flan in a tin with a removable bottom, then again, I've never made flan so I don't know, but isn't it liquid?
I bake my tarts on a cookie sheet just in case there's any leakage, and so that it's easier to remove from the oven, otherwise it's just too small to grab.
I'm curious too. Just bought a cheapo one from Target, labeled as tart & quiche pan, to make an apple tart. The bottom was a removable circle, I guess to make removing the dish easier. Are all of 'em like this? Almost burned myself, as the the outer ring dropped down my arm as I was removing it from the oven. Maybe I'm just lame.
Yeah, that'll get you the first time or two. You can push up from the bottom to get the tart out and then you have a nice tart with the sides exposed. It is a trick to remember to hold it from the sides or support it from the bottom when you are taking it in and out of the oven.
I think of tart and flan pans as being shallow and having the removable bottoms. Not sure about quiche pans as I think of them as deeper and not necessarily having the removable bottom. But others may know differently about that.