You got it. To some purists, Linux is just the kernel and everything else is strictly another body of work, but thankfully the purists don’t dictate things. The rest of us usually mean “A Linux Distribution”, of which Ubuntu is the most popular on desktops. Popular distros on servers would include Debian (Ubuntu’s parent distro), Amazon Linux (used on AWS, mostly CentOS based) and Alpine (an original distro mostly used in Docker containers).
Different distros aren’t even perfectly compatible with each other unless the app is completely static (fairly difficult nowadays), but the kernels are compatible, so as long as you have all the right support libraries installed for the distro, any linux app will work on the other – though it wasn’t until Docker came on the scene that this portability became practical and useful.