pp. Delivering video programming aimed at an extremely small audience.
Other Forms
Rocketboom's popularity makes it a poster-child for "slivercasting" in which video programming can be easily and inexpensively delivered to a niche audience — something that is a huge challenge within the traditional broadcasting industry.
—Mark Evans, “'Slivercasting' a hit with savvy set,” The National Post, March 25, 2006
In the last six months, major media companies have received much attention for starting to move their own programming online, whether downloads for video iPods or streaming programs that can be watched over high-speed Internet connections.

Perhaps more interesting — and, arguably, more important — are the thousands of producers whose programming would never make it into prime time but who have very dedicated small audiences. It's a phenomenon that could be called slivercasting.
—Saul Hansell, “Much for the Few,” The New York Times, March 12, 2006
1982 (earliest)
That's bad news for those who have high hopes for "narrowcasting," material aimed at small audiences interested in specific programs and, therefore, prime audiences for specific products — fitness, business, cooking, you name it. As 50- and 100-channel systems come into being, narrowcasting could become slivercasting. A shrinking audience will limit advertiser interest.
—Thomas O'Donnell & Jay Gissen, “A vaster wasteland?,” Forbes, May 24, 1982