What does it mean to be a full-stack developer?

You can imagine any software product to be built in a series of layers, one stacked upon the other. You begin with the most fundamental and abstract elements and then build on top of those things like attractive UIs and flourishes like animations. 

In the case of web development, this is more complex because you’ll need to manage servers and databases and you’ll need to make sure all that private data is secure. Each of these elements can be considered layers in a stack. The full-stack developer then is someone who understands every layer instead of just their narrow slice.

“Think of the full-stack developer as a “Jack of all trades”, who may still specialize in one area.”

They are a much more valuable part of the team and also much more capable of working independently. 

It’s like having a kitchen full of chefs, sous chefs, apprentices, and other professionals. There’s only one head chef, but you would expect an apprentice to be able to do basic jobs like boil some pasta. And life would go a lot more smoothly if they understood which dishes required the pasta to be “al dente” and which ones required something a bit sloppier. But this is really just a very simplified example. 

In reality, the term “full-stack” is only applied to web-based apps which have much more complex stacks.