what is ‘alpha’ and ‘alphadash’ - development

what is ‘alpha’ and ‘alphadash’

I recently encountered a part of PHP code right below:

$this->validate($request, [
   'name1'->'required|alpha|unique:users',
   'name2'->'required|alphadash'
]);

the question what is ‘alpha’ and ‘alphadash’ and what happens when I using them in middle of my coding?

from Laravel Questions and Answers https://laravelquestions.com/php/what-is-alpha-and-alphadash/
via Lzo Media