I only used the term 'folder', instead of 'directory' as that is what most users are used to these days, if they are using some sort of GUI. The term 'directory' tends to be more familiar to those who regularly access them via the command line (which is generally a smaller minority, who are also more able to cope with understanding that directories & folders are the same thing).
As for explaining aliases to teachers, you could try getting them to read http://docs.moodle.org/26/en/Working_with_files#Creating_an_alias.2Fshortcut
Or you could just go through the steps with them (or even better, let them try as you talk them through):
- create a 'folder' resource with a file in it
- create 2 'file' resources in the same course - 1 as a 'copy', 1 as an 'alias / shortcut'
- overwrite the file in the 'folder' resource
- demonstrate that the first 'file' resource is unchanged and the second has now updated