A fatal error.
Someone's pager is going off at 2:00 in the morning because the nuclear codes have gone off and missiles have been launched.
A normal error that cause usually be recovered from.
May require a fire being put out or some immediate response, but it is not world ending.
Some information that's good to know.
Analytic logs are in this zone and general information goes in this zone. Debug as well, goes into this zone.
It is normally best to avoid this log level unless it's really important to display.
Nothing is really wrong.
Should probably not be ignored and action should be taken, but it's not serious enough to call the fire department.
The log level.