What does a dot in file permissions signify - Linux?

What does a dot in file permissions signify? As in rwx rwx rwx.

Following the file mode bits (rwx) is a single character that specifies whether an alternate access method such as an access control list applies to the file. When the character following the file mode bits is a space, there is no alternate access method. When it is a printing character, then there is such a method. 

GNU ‘ls’ uses a ‘.’ character to indicate a file with a security context, but no other alternate access method. 

A file with any other combination of alternate access methods is marked with a ‘+’ character.