When people say &quot;full stack&quot;, it means something very specific to me.<p>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.<p>Certainly when hiring for &quot;back-end developer&quot;, I expect deep knowledge of OS- and DB-level concepts like indexing and garbage collection.<p>Likewise, when hiring a &quot;front-end developer&quot;, I expect deep knowledge of various mobile, desktop and tablet devices and the behavior various browsers exhibit on them.