[YuriNiyazov]

When people say "full stack", it means something very specific to me.

It means you can do both UI and server code, so you have a wide variety of knowledge in the many competing front-end and back-end frameworks out there, but you are not quite an expert in anything. At your last job you learned all the magic incantations of jQuery, Rails and MySQL, but but today you are expected to learn all the magic incantations of React, Node and Mongo. Specifically because you are expected to change your toolkit quickly, you do not dedicate any time to scratching the surface.

Certainly when hiring for "back-end developer", I expect deep knowledge of OS- and DB-level concepts like indexing and garbage collection.

Likewise, when hiring a "front-end developer", I expect deep knowledge of various mobile, desktop and tablet devices and the behavior various browsers exhibit on them.

[ChemicalWarfare]

"full stack" is definitely an overloaded term but then again I wouldn't consider the kinds of questions OP mentions to be something only the experts would (or should) be able to answer on the basic level.

Things like get vs post, encoding, basic headers (like accept etc) should be familiar to anyone dealing with the client side development regardless of the tools/frameworks.

And then on the backend some basic SQL, basic understanding of indexing, FKs, PKs, maybe simple inner joins is also something that someone doing anything DB-related on the backend should be familiar with (unless we're talking someone who is only familiar with nosql dbs) regardless of the tools/frameworks/orm etc.