Most people use stable to refer to something that doesn't crash or cause issues. Something that you might call "rock solid" which implies it's not going to fall over. Something to put on your server because you'll get great uptime without issues.

Debian is one of the few places where stable might crash more than unstable, because known bugs in Debian don't get backported unless they cause security issues.

I use Debian on my servers because "some testing" is nice and the only thing I run on my servers is docker. And ironically, I have to use a PPA for docker.

So for me, it's a stable enough base OS, but it "too stable" for anything that actually runs on the servers.