On the Docker Hub site, I find tags "rolling" and "latest". What is the difference between them?
From the linked page:
ubuntu:latesttag points to the "latest LTS", since that's the version recommended for general use. The
ubuntu:rollingtag points to the latest release (regardless of LTS status).
The current "latest" and "rolling" release is 18.04 LTS. The next "latest" release will be 20.04 LTS; the next "rolling" release will be 18.10.
ubuntu:latest means the latest LTS release - as of writing this comment, that would be Ubuntu 18.04 LTS. Next LTS will be Ubuntu 20.04 LTS in 2020.
ubuntu:rolling means the latest release regardless of LTS status - as of writing this, that would be Ubuntu 18.04 - until Ubuntu 18.10 comes out in October.
LTS is generally more stable and less likely to have features break, but also has older versions of software.