Just what it says. Do they have a name besides "those dot thingies"?
They're called directory abbreviations.
. = current directory
They're normally called 'dot' and 'dot-dot' in my experience. I don't know that they have a collective name - they're just the entries that hold the hierarchical file system together, and they aren't shown by '
As John T says, they're meanings are fixed - dot is a name for the current directory, and dot-dot is a name for the parent directory.
If you look at a Unix 7th Edition manual, you'd find that there wasn't a