I’m not the best person to explain, but they’re distros with a read-only root filesystem. In some implementations, any changes, like installing a new package, or upgrading a version, can be interpreted as migrating a system from a state to another. This can mitigate some security risks and make machines easier to maintain.
Perhaps this will change drastically with immutable distros
What is immutable distros?
I’m not the best person to explain, but they’re distros with a read-only root filesystem. In some implementations, any changes, like installing a new package, or upgrading a version, can be interpreted as migrating a system from a state to another. This can mitigate some security risks and make machines easier to maintain.
Check fedora atomic builds. They explain it very well.