What does it mean to die by 'natural causes?'

Texas officials have said that Supreme Court Justice Antonin Scalia died at age 79 Saturday of "natural causes."

But what are natural causes?

The term rules out deaths that are due to "any type of injury or foreign substances," said David Fowler, president of the National Association of Medical Examiners

For medical examiners, Fowler said, there are five main categories of deaths: homicide, accident, suicide and natural causes and "undetermined."

The broad category of natural causes could include any number of specific diseases that can lead to death, from cancer to heart conditions.