I was organizing some old study notes and came across this mnemonic. It's easy to remember, and I'm sure many network engineers can relate.
Everyone always complains even when nothing is different.
[E]veryone [A]lways [C]omplains [E]ven [W]hen [N]othing [I]s [D]ifferent
[E]mergency [A]lert [C]ritical [E]rror [W]arning [N]otification [I]nformational [D]ebugging
Level Description
0 - emergency System is unusable
1 - alert Immediate action needed
2 - critical Critical condition
3 - error Error condition
4 - warning Warning condition
5 - notification Normal but significant condition
6 - informational Informational message only
7 - debugging Appears during debugging only
More information about syslog (system message logging):
https://www.cisco.com/c/en/us/td/docs/routers/access/wireless/software/guide/SysMsgLogging.html