This is from
Cisco.com and probably a better explanation.
And i understand this isnt a cisco device but its a protocol (defined in RFC 3164)
Facility
Syslog messages are broadly categorized on the basis of the sources that generate them. These sources can be the operating system, the process, or an application. These categories, called facility, are represented by integers, as shown in Table 4-1. The local use facilities are not reserved and are available for general use. Hence, the processes and applications that do not have pre-assigned facility values can choose any of the eight local use facilities. As such, Cisco devices use one of the local use facilities for sending syslog messages.
Table 4-1. Facility Values
Integer
Facility
0 Kernel messages
1 User-level messages
2 Mail system
3 System daemons
4 Security/authorization messages
5 Messages generated internally by Syslogd
6 Line printer subsystem
7 Network news subsystem
8 UUCP subsystem
9 Clock daemon
10 Security/authorization messages
11 FTP daemon
12 NTP subsystem
13 Log audit
14 Log alert
15 Clock daemon
16 Local use 0 (local0)
17 Local use 1 (local1)
18 Local use 2 (local2)
19 Local use 3 (local3)
20 Local use 4 (local4)
21 Local use 5 (local5)
22 Local use 6 (local6)
23 Local use 7 (local7)
By default, Cisco IOS devices, CatOS switches, and VPN 3000 Concentrators use facility local7 while Cisco PIX Firewalls use local4 to send syslog messages. Moreover, most Cisco devices provide options to change the facility level from their default value.
