What does it mean if something is fluted?

When an object is described as fluted, it means that it has a series of grooves or ridges that run along its surface. This term is often used in various contexts, such as in architecture, where columns can be fluted to add visual interest and texture. Grooved surfaces can enhance the grip or aesthetic appeal of an item, like in the design of glassware or furniture.

In contrast, the other options suggest a lack of texture or design; a smooth surface would be free of any irregularities, a flat surface is level without any elevation or depressions, and a plain surface lacks decoration or embellishment. Therefore, the characteristic of being fluted distinctly relates to the presence of these grooves, confirming that the correct interpretation of fluted is indeed grooved.