The command ll (lowercase 'L') is not a native Linux command, but it is included in most distributions. ll is an alias for the ls -l command. Since ls -l is frequently used, using ll as a replacement for ls -l is more convenient.
Example:
| $ ll /etc/*.conf -rw-r--r--. 1 root root 55 Mar 1 2017 /etc/asound.conf -rw-r--r--. 1 root root 14392 Aug 4 2017 /etc/autofs.conf -rw-------. 1 root root 232 Aug 4 2017 /etc/autofs_ldap_auth.conf |