[dba-SQLServer] about password_hash

Can someone explain the password_hash column in the sys.server_principals 
catalog view. My guess is this hasn't a thing to do with the actual password 
you assign to individual users and that it has something to do with 
synchronizing or security, but I don't really understand it.

Where can you find a list of "assigned" passwords or is that information 
available?

Susan H.