The general definition is any health problem that lasts more than three months and significantly affects a child and his family.
Children who have chronic medical, developmental, behavioral, or emotional conditions are collectively defined as “children with special health care needs” (“CSHCN” for short, which makes for easier writing but doesn’t do much for talking). This widely adopted term is now used to identify all kids who need extra health care, regardless of their condition. Yes, I know, this definition seems absurdly broad. A child with severe cerebral palsy who needs constant care and a child with moderate asthma who needs to keep an inhaler handy are both considered CSHCN.
From The Smart Parent's Guide: Getting Your Kids Through Checkups, Illnesses, and Accidents by Jennifer Trachtenberg.
Find out more about this book:The Smart Parent's Guide: Getting Your Kids Through Checkups, Illnesses, and Accidents