Good question! Then again, I always say that there is no such thing a dumb question unless it is one that is never asked. So all questions are good questions! They just don’t always have easy answers.
And this question is best answered with “It depends” …
It depends upon where you live, what those who raised you called it, and so on.
Actually they are all pies. Usually. Terms just vary as an attempt to describe which type of pie.
In the U.S.A., the terms used — generally (but not always) — mean the following:
A dessert pie is sweet (a dessert) and has a bottom — usually a buttery, flaky shortbread pie pastry crust, but it may also have a cracker or cookie crust. It may — or may not — have a top crust.
A tart is another term for a topless pie — but can also be used generically for any pie or pastry.
A pastry usually refers specifically to a dough — but sometimes it is used synonymously with the term tart — and therefore can refer generically to any type of pie or dessert which involves the use of a dough.
A savory pie (non-dessert) usually — but not always — has both a bottom and a top. Sometimes, they just have a top — or (more rarely) just a bottom.
Usually, in the U.S.A., a savory pie is called a pot pie — unless it is a savory hand pie.
Pot pies, especially in southern states, may be topped with cornbread.
Additionally, they may be topped with a buttery, flaky shortbread pie pastry crust, dumplings, biscuits, puff pastry, filo pastry, as well as pizza crusts or other leavened breads. They may also be topped with cracker (unleavened bread) crumbles or croutons.
If it is a savory casserole topped with mashed potatoes it is called a Shepherd’s pie.
Sometimes, mashed potatoes are put on the bottom and it is called an Upside Down Shepherd’s Pie.
A hand pie (which has many other names — i.e. such as empanada and pastilla) may be sweet or savory. They may be baked or fried.
It is when a small circular crust is filled and folded in half to form a semi-lunar shape.
If it is a folded over pizza pie, however, made with a standard pizza crust and savory fillings, then it is referred to as a calzone.
A cobbler is sweet (a dessert) and has no bottom crust but it is topped.
This is the official definition also used by culinary schools and chefs. It is also the most commonly used definition.
Now things start to get a bit tricky.
For some, however, a cobbler means any pie with a fruit or berry filling — instead of a custard or other kinds of fillings — so it may have a bottom crust in such cases. So, you have the majority calling it a fruit pie if it has a bottom — but there are others also calling any fruit or berry containing pie a cobbler.
A cobbler usually contains fruits, berries, or rhubarb. It may contain only one of these items or any combination. And it has a top. On that, at least, everyone agrees. It’s just the lack of a bottom crust that sometimes becomes a grey area.
The top of a cobbler may be made of a shortbread pie pastry crust, dumplings, biscuits, cookies or crackers (usually crumbled up but not always), or even cake batter (usually, but not always, spooned on in dollops). It may even have a crumb topping — although then there is the issue of whether it is still a cobbler type of pie or if it has become a crumb (streusel) or crisp — but more about this later.
For cobblers, the top usually has gaps whether it is a latticed shortbread pie pastry crust, or it has been dotted with spooned on or dropped on biscuits, dumplings, or cake batter, etc. — unless it is actually a pie with rhubarb, fruit, or berry filling which may have a solid top crust — but some will argue that even with top crust which has slits cut into the crust it still qualifies as a cobbler simply because of the type of filling. Additionally, some argue there is no such thing as a rhubarb cobbler — that there is only rhubarb pie — or a fruit or berry cobbler with rhubarb.
There are some instances in which a solid thin layer of cake batter is used for a cobbler. However, if there is more cake than filling, it becomes an upside down cake instead of a cobbler and is no longer actually a pie.
If it is sweet (a dessert), and contains fruits and/or berries, and it only has a crumb (streusel) topping then it is usually referred to as a crumb or a crumble. It may also be called a streusel. It may be lightly sprinkled or heavily coated, but even if heavily coated cracks occur during baking allowing the filling to seep through.
There are many types of crumb toppings.
Some are made with flour, and others with things like oats or crushed cookies or crackers, but they all usually — but not always — have a sweetener mixed in such as sugar, brown sugar, honey, molasses, other syrups, etc. and may or may not include seasonings.
Most crumb toppings are toasted in the oven (either separately or on top of the cobbler as it is being baked), but some are not toasted at all.
Depending upon the ingredients used, the quantity of sugar, and the temperature at the time eaten, the amount of juices/syrup absorbed, and so on — the crumb topping may be soft, crispy, or even crunchy.
Crisps are desserts (usually fruit — but sometimes berries or a combination) with a very crispy, very sweet crumb topping. Usually, to be considered a crisp, the crumb topping also contains toasted nuts and/or other toasted items such as granola as well as flour plus sugar or another sweetener. It is also a much less frequently used term.
The term crisps also has many other meanings — however, there are far too many to get into here.
Too much sugar, however, and crisp or crumb toppings may even become like hard candy as the initially soft heated and melted sugar cools and then solidifies into a brittle.
Correct proportions of the sugar to other ingredients is important in determining how it will turn out after it begins to cool and whether you have a soft, a lightly crispy, crispy, or crunchy topping — or a hard one that could chip a tooth.
Generally speaking, if a cobbler has a crust on bottom and a crumb or crisp topping then it is still a cobbler and therefore it is a type of pie — although cobblers generally do not have a bottom crust.
If there is no bottom crust and it only has a crumb or crisp topping, then it may (or may not) be referred to as a crisp, crumb, crumble, or streusel — but it is still considered a cobbler — but it may or may not (usually not) be considered a pie. Yet, a cobbler is usually considered a type of pie.
In the end, no matter what they are — or, are not — called, they are all fabulously delicious!