It’s kind of a gray area. If you do something that kills someone and a reasonable person could not have foreseen the possibility of the death, then it’s just an accident. They don’t need a term for it because you won’t be prosecuted. This would be like if you gave someone a banana and they ate it and died and neither of you knew that they had a banana allergy.

Manslaughter is when you could have reasonably foreseen the death before you did the thing that caused the death. This would be like driving too fast on a wet road losing control and killing your passenger.

Third degree homicide is a step beyond that. You are doing something that you know is stupid at this point. This would be like driving with a blindfold on and crashing and killing your passenger.

Second degree is when you know that what you’re doing is very likely to kill someone. This would be like shooting a gun down a crowded street, aiming at a tree, but hitting a person and killing them instead.

First is when you kill somebody and you meant to kill them. Obvious.

All the examples I gave could arguably be in an adjacent category depending on the exact facts. It all has to do with the mental state of the person who is doing the dangerous thing. What did they mean to do? Could they have reasonably foreseen that what they are doing could result in a death? Factors like intoxication, mental illness, and emotional disturbance all affect a person’s mental state. There is nuance to that as well. If you know you become violent when you get drunk then you are less likely to successfully convince a jury that you didn’t know what you were doing. Some people get drunk or high to give themselves the nerve to commit a crime.