Stacks are organization specific. Wikipedia's definition at https://en.wikipedia.org/wiki/Solution_stack is nice.
For fun: https://trends.google.com/trends/explore?date=all&geo=US&q=L...
On my Job Board for Full Stack Developers ( https://fullstackjob.com ) I try to handle it the way, that requirements are on both "sides", back and front end at least. That's not exactly my point of view, but the only common denominator I can see.
What I can see from job submissions on my side project https://fullstackjob.com is, that for at least 50% of posting companies/recruiters, Full Stack is "just a bunch of skill's". For mostly all of them it includes both Front- and Backend. SOme of them include DB knowledge, but not always clear, if they mean "just query lang" or DBA skills.
In my opinion, when I hire somebody Full Stack, it is mainly about the fact, that this guy then can understand a complex software from front- to back and forward, but not that he can develop the whole thing.
I'm a little confused about what you are asking...
What I look for in resumes are:
1. Do they have any projects I can review (preferably open source and on github)
2. What frameworks are they familiar with
3. How much experience (often signaled by the frameworks)
4. Do they have experience managing databases, cloud infrastructure, front end, etc. Also, usually signaled by the frameworks
A lot of architectures are simply divided into front-end and back-end, but not all, and there's often ancillary systems involved (such as caching, external data imports, etc).
It means you aren't a specialist - you can work on anything.
This is very hard, and does not scale long term depending on the product.
On the contrary, there are people who specialise in specific things. So you might specialise in database issues and want to work primarily on the back end. Or you might specialise in UX, etc and want to specialise in the front end. Some very junior people have only been exposed to programming in very limited situations (for example writing some javascript and knocking up some HTML) and may want to advertise that this is what they are comfortable with for now, so may call themselves a "Frontend developer"
Some hiring managers/companies believe that there is a class of programmer who can do "simple" things and take the load off the general programmer. They feel they can hire this class of programmer and save money. My experience is that this doesn't ever work out. It's fine to hire junior people who become full stack developers eventually, but hiring someone who lacks the ability/interest to take it further usually costs more in productivity than they save in salary. I really don't like this idea of trying to hire "Frontend developers" as a kind of "lesser programmer" (as opposed to specialists programmers who just want to concentrate on UX).
The TL;DR: "Full Stack" just means "programmer" in my books.