So, how can I make links "absolute" to simply write [[Rock]], and whichever page that link i into, it will link to the only existing Rock page?
This links always to the Rock-Page in the root-namespace:
[[:Rock]]
It is the central concept of namespaces (private spaces for names) that there can not be just one page called "Rock". And for that reason, there is no addressing method that would address this one page.
Namespaces are commonly structured as hierarchies to allow reuse of names in different contexts.
Source:
https://en.wikipedia.org/wiki/Namespace
I advise every beginner to be really sparing with the use of namespaces. If you only use namespaces to get a certain clarity, then you make IMHO probably a mistake. There are many more flexible ways to structure your wiki, eg. tagging. My impression is that namespaces are applied too often. This seems to be a quick fix, but it also has consequences that you should be aware of.
BTW: All normal articles/pages in a given language in Wikipedia belong to the same namespace.