Melee diamonds are tiny diamonds used in diamond jewelry, often used to accentuate a single center stone on an engagement ring.
The little diamonds used for settings like a halo, pavé or channel setting? These are almost always melee diamonds.
Officially, the Gemological Institute of America (GIA) defines melee diamonds as diamonds that are less than 0.2 Carats. While this is the biggest melee diamonds get, they can come as small as 0.001 carats.
A melee diamond is very small and thus not much on its own. However, a group of melee diamonds clustered together can add a stunning sparkle to an otherwise plain ring.