Aliases in Joomla! CMS are short fragments of text that indicate the name of certain elements (menu items, materials and categories) in machine format. This format allows only lowercase letters, as well as underscores (_) and hyphens (-).
In Joomla! CMS of all versions there are 2 ways to fill in an alias:
Automatic
Applies if the text field for the alias is left empty.Manual
Manual filling of the text field for the alias.
FYI
All invalid characters in the alias field will be removed when saving.