"Full-Stack Developer" is a term derived from the term "Application Tech Stack", which is a term used for a comprehensive description of all the major tech used

"Full-Stack Developer" is a term derived from the term "Application Tech Stack", which is a term used for a comprehensive description of all the major tech used to deliver an application. A Full-Stack Developer is capable of working through the entire Application Stack. It's a relative term, relative to the technology you work on and the domain you work within. Many components in the stack are off-the-shelf. It's tricky when talking about SPAs because while we call SPAs "applications" they almost universally are only thin-client frontends over an API. I wouldn't call the Washington Post's frontend an actual application, nor would I call the Mixpanel UI an application. It gets fuzzier with things like Slack and Spotify. Personally, when I hire, I only hire full-stack web developers and my expectation is that they're just as comfortable rendering HTML on the backend as the frontend (and they have a pragmatic sense for what is appropriate when), they have no problems manipulating the underlying database schema, they can manage the caching system, jobs system, email delivery, etc. Not everyone is amazing at everything but everyone needs to be familiar and moderately comfortable doing most things, and the team is there to backfill anyone's personal gaps.