Ovolo (or ovulo) in architecture, is a convex molding known also as the echinus, which in classical architecture was invariably carved with the egg-and-dart ornament. The molding is called a quarter-round by woodworkers. This is not to be conflated with the "echinus" of the Doric capital, as this was of a more varied form and of much larger dimensions than the ovolo, which was only a subordinate molding.
This edge profile is commonly used as the inside profile edge of stile and rail interior doors and cabinetry doors. The concave cavetto molding is the opposite of the ovolo.
The term ovolo is often used to describe the type of architectural structure often used in huts, igloos, and mud brick houses.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Ovolo". Encyclopædia Britannica. 20 (11th ed.). Cambridge University Press. p. 391.