There are no permissions set for the file.

Execute/search permission, owner

Read, write, execute/search by owner;
owner_read | owner_write | owner_exec

Execute/search permission, group

Read, write, execute/search by group;
group_read | group_write | group_exec

Execute/search permission, others

Read, write, execute/search by others;
others_read | others_write | others_exec

owner_all | group_all | others_all

Set-group-ID on execution

Operating system dependent.

all | set_uid | set_gid | sticky_bit

The permissions are not known, such as when a file_status object is created without specifying the permissions