A woman working on a book blurb approached us about the story behind the term cameo appearance. We wish she'd asked instead about blurb; we can easily pin that term for "a short publicity notice" on humorist Gelett Burgess, who remarked, "On the 'jacket' of the 'latest' fiction, we find the blurb; abounding in agile adjectives and adverbs, attesting that this book is the 'sensation of the year.'" (来源：英语杂志 http://www.EnglishCN.com)

Alternatively, our questioner might have inquired about the cameo that names a gem carved in relief and refers particularly to a small piece of sculpture on a stone or shell cut in relief on one layer with another contrasting layer serving as background.

In fact, this cameo (which entered English via French in the 15th century) gave us the cameo under glass today. The concept of something highlighted, or shown in sharp contrast, eventually cropped up in literature. During the 19th century, cameo began being used to describe a usually brief literary or dramatic piece that brings into delicate or sharp relief the character of a person, place, or event.

Over time, and with the advent of film and television, cameo was adapted to refer to the small theatrical role usually performed by a well-known actor and often limited to a single scene, or, more broadly, to refer to any brief appearance or role.