A seminar caller is a coined phrase for someone who mainly telephones conservative radio talk shows for the purpose of astroturfing, which is the mass promotion of a particular product, service, or opposing political point of view as if it were genuinely spontaneous, or grassroots.
Many of these supposed seminar callers try to portray themselves as regular people, claim to agree with the host's point of view, then begin to read a contrary opinion from an agenda or list of talking points widely circulated by a group or organization who oppose the views of the host.
Seminar callers get their name from the seminars they supposedly attend to learn how to most effectively get their message on the air. There is no evidence that seminar callers actually attend seminars for this purpose. Faxes, e-mails and newsletters are more common modes of disseminating astroturf messages to seminar callers.
Before the 2004 U.S. presidential election, seminar callers began to tell more elaborate stories to establish credibility, behaving as if they were actors playing the role of someone with beliefs opposite of their own, in an attempt to erode the opposing candidate's "base" of political support.
The term "seminar caller" is in wide use among talk show hosts and audiences.