In the context of ornaments/design, Acanthus refers to a design in which leaves that resemble the acanthus plant (a common plant of the Mediterranean) are carved/chased on an object such as silver in order to embellish and decorate the surface of the item.
The leaf and scroll-like motifs were extensively used in architectural works during the Greek and Roman periods, however, during the Victorian era, the motif was prevalent amongst silverware in decorating snuffboxes and the likes.
The symbolism is often debated - one meaning associated with this plant is that of a long life/immortality in Mediterranean nations.
In many cases, the design of the ornament will differ greatly to the actual plant's leaf as the idea/concept of acanthus leaves have been utilised loosely with much modification in design and shapes - you will often see more of a curved/scroll-like design in victorian acanthus motifs.
An acanthus based motif used on a Victorian silver snuff / vinaigrette box.