[all variants] can see file using ls, but can't see the content using less

Well, this time it worked.

ls -l /u01/t1/admin/ef/log/tr.txt
-rw-r--r-- 1 t1 oinstall 10120 March 23 17:10 /u01/t1/admin/ef/log/tr.txt

As I can see (if I do everything correct) the error happens from time to time somehow.
Will check later to catch the error and will update here.
Can you tell me what these rights -rw-r--r-- mean?
Thanks.