Sinus

Sinus is Latin and means curvature, rounding or arc. In botany this refers to the area between the two "leaf ears" (lobus). The shape of the sinus depends largely on the shape of the lobe.
The shape and structure of the sinus and lobes can vary greatly among different Anthurium species and cultivars and are often used for differentiation and classification.

While some anthuriums and anthurium hybrids have simple, smooth and flat sinus lobes, such as the A. sp. Nov. 'DF', others form complex lobes in round or ear-like shapes.