ntn888 Pages on a MediaWiki wiki are grouped into collections called "namespaces"
Namespace is a space for name.
It comes from computer language definition where each variable/data has a name.
In a broader definition, it is a way to group thing (ie name) and to give them a scope (or context as @saggi said).
You will find this concept in all data modeling structure
Because Dokuwiki creates a file for each page and is based on the file system, the namespace is just the directory path.