What is "trilobular"

Trilobular (formed from tri, Greek for three and lobus, Latin for tabs) describes a geometric shape that can be described as a "triangle-round". It is characterized by the fact that in spite of its triangular-like shape, its roll diameter is constant because a large and a small rounding face always oppose each other. Its is therefore a curve of constant width. The measure of Trilobularity is given as a ratio between the inscribed and circumscribed shape.