Danger rating is a classification that is used to measure how dangerous a species is.
Harmless: It wouldn't/couldn't hurt a human.
Minimal threat: It can do minor damage to a human; small scratches & bites, etc.
Medium threat: It can do considerable damage to a human; large scratches, moderate bleeding, etc.
Significant threat: It can do severe damage to a human; broken bones, severe bleeding, etc.
Extreme threat: It can maim a human; severed limbs, major blood loss, etc.
Lethal: It will kill a human on sight.