system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does it mean to die of "natural causes?"
gpt
It's mostly a distinction used in the legal profession. Technically being eaten by a lion is a very natural way to die, but we wouldn't call that natural causes.  

A cause of death can be accidental, murder, disease, or natural causes. 

Accidental is you fall off a bridge. 
Murder is somebody pushed you. 
Disease would be something like cancer. 
Natural causes would be something like heart failure due to advanced age or declining health. 

We have a limited life span and as you get older, the chances of you not recovering from an illness go up. A 40 year old may have the strength to fight off a cold, but an 80 year old may not. 

From a legal stand point, natural cause is a blameless death where as accidental, disease, or murder would have a cause and somebody or something to blame (even if it's yourself).