Not What You Think
One of the most challenging things about using English well is that it is a huge mesh of words, with many overlaps and intersections and many close-but-not-quite relations. Part of this massive web is a large collection of categories--words that describe collections of other words--and if you choose the wrong category, if you call the Sun a planet, then people who know better are going to think less of you.
Here is a sentence from a Slate article about the apparently never-ending cupcake boom:
...we must turn to TV for signs that this madness must stop. It was here, after all, that Sex and the City—without reference to which no cupcake article is complete—transformed the pastry into a totem.
The thing, though, is that a cupcake is not a pastry, and here the reader gets the unfortunate sense that the writer was simply grasping for unnecessary variation to keep from saying "cupcake" one more time (why?).
A cupcake, like a muffin or a torte, is a cake, made from batter, which is a liquid. A cookie or a bread is made from dough, which is a fluid--stiffer than a batter but a fluid for all that. A pie, a danish, a cream puff, or a baklava is made from a paste of flour and water and fat (although in the case of baklava the fat is applied after the fact): paste = pastry. It's right there in the etymology!
Some people use "pastry" as a categorical term for "any baked sweet confection": bread pudding, zweiback, macaroons, blonde brownies--pastry, every crumb of it. Other people think that it doesn't matter either way, that people like me are making a mountain out of a molehill. All those people are wrong. They're probably just as comfortable calling a frog a reptile or an AK-47 a pistol.