The internet is, without metaphor, just a bunch of servers tied together with wires. Without servers, we'd have no way to share our creations with the world. Yet, in a bit of a paradox, servers are <em>less</em> essential to our work than they've ever been. We can now do things on the front-end that used to require a back end. When we do need a backend, our front-end skills can be put to work, giving us some surprisingly powerful new abilities.
It's kind of a phenomenon. Let's get one thing out of the way: it still involves servers, so that word serverless might feel a bit disingenuous. It's actually a new way to pay for and work with servers that, in many cases, is cheaper and easier than buying and managing your own servers.
Web developers of all kinds can take advantage of it, but this site is particularly interested in how it relates to and helps front-end web developers. Here's one way to think about it: you can take your front-end skills and do things that typically only a back-end can do.