(CNN) -- Singer George Michael died last year of natural causes, a coroner announced this week.

But what does that phrase "natural causes" mean? Or, rather, what is "unnatural" about something that happens to everyone? Is it just for the old? Does cancer count as "natural?"

The answers are more complicated than the simple, common phrase would lead many to believe, and they even have legal ramifications.

For Michael, 53, the "natural causes" were a heart condition known as dilated cardiomyopathy with myocarditis. He also had a fatty liver, according to Oxfordshire's senior coroner Darren Salter.

Here is a look inside the process doctors go through to determine whether a death was "natural," and what exactly that means (or doesn't).

What are 'natural causes'?

It might not seem to mean much at all. But when a death certificate says a person's death was "natural," it is really ruling out the involvement of external causes. The person did not take their own life and they were not killed by somebody else or in an accident such as a car crash or drug overdose.

"It's solely and exclusively due to natural causes, a natural disease process ---infection, cancer, heart disease, all of those things that are going to carry us off at some point along the way," Fowler said.

Death certificates almost always include more details about specifically how the body failed, such as heart disease or kidney failure, even if it is only the best guess of the coroner (a trained official) or medical examiner (a doctor) charged with investigating the death.

"When a medical examiner fills out a death certificate, it's their medical opinion based on all their experience and training that this is what happening," said Dr. David R. Fowler, president of the National Association of Medical Examiners.

"You're rather like a judge. You weigh the evidence, and based on the predominance of evidence you come to a decision that I think this is what caused the problem, but I'm going to be an honest person and list all these other causes," Fowler said. These other causes appear in a second section of the death certificate for potential contributing causes.

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