hard to explain!!
Go to Google type in "define: flan" (no quote marks though, and don't forget to put a space between the colon and the word flan). Then do the same for quiche.
In Britain, both flans and quiches have pastry cases; but the former usually have a sweet filling, and the latter savoury. (Also, a flan often has a criss-cross of pastry strips on top.) However, on the Continent - especially Spain where it is a very popular desert - flan (plural: flanes) is a creme caramel, without any pastry.