File with a + (plus) sign in a permission contents list.

Hello everyone. A couple of months ago I've created a simple 'notes' file in my home directory. This file was designed to contain various informations, notes etc. Nothing more, nothing less. However, I've noticed, that mentioned file have a "+" sign in a permission contents (there also could be a 't' letter, which means 'sticky bit' etc.):

,-----[ $ ls -al /home/tester/ ]
| -rw-------+ 1 tester tester 37592 sep 15 19:15 notes
`-----

Honestly, there is not to much information on the web about file name with a "+" sign. However a couple of weeks ago I've tried to set an ACL (Access Control List) permission with a 'setfacl' etc. command. Could it be related with my question? Unfortunately I've not much time to check it again - I mean setting an ACL permission on some file.

Does anybody know something about "+" sign in a file information?

Best regards.