Zebra is quite a basic term in general medicine but especially in pediatrics.
It refers to a disease or condition that is very rare. Now, since 99% of conditions are trivial and have a common presentation, the term ‘zebra’ refers to an exotic and rare condition (Dr. House style) that could have brought about the same medical condition.
Nonetheless, the term ‘zebra’ will be most commonly used during a medical discussion about a patient with a complex presentation, when one of the physicians will suggest a very rare disease as the diagnosis and another will reply “come-on, that’s a zebra”.
The term originates from the saying “When you hear hoofbeats behind you, don’t expect to see a zebra”