Today's diamond fact of the day isn't really a "fact" per se, but more about learning terminology. Let's learn some words:
When talking about a diamond's cut, the "fire" represents the flashes of color you see in a polished diamond.
"Scintillation" - This refers to the flashes of light and the contrasting dark areas you see when the diamond, the light, or the observer moves.
"Unplanned light leakage" - This refers to the light that escapes through a diamond's pavillion and weakens its display of light.
A well cut diamond has excellent fire, excellent scintillation, and minimal light leakage. It's the precision of the angles of a diamond that allow maximum light to be refracted and shot out the table.