What is a spillway space or embrasure?

Definition - When two tooth in the same arch are in contact, their curvature adjacent to contact areas form spillway spaces also called embrasures. The spaces that widen out from the area ne contact labially or buccally and lingually are called labial or buccal and lingual inter proximal embrasures.

The embrasures are continuous with the inter proximal spaces between the tooth.
Above the contact areas incisally and occlusally, the spaces which are bounded by the marginal ridges as they join the cusps and incisal ridge are called as the incisal or occlusal embrasures.
Incisal or occlusal embrasures, and the labial or buccal and lingual embrasures are continuous.