Spamigation is mass litigation conducted to intimidate large numbers of people. The term was coined by Brad Templeton of the Electronic Frontier Foundation to explain the tactics of the Recording Industry Association of America (RIAA), which files large numbers of lawsuits against individuals for file sharing, and DirecTV, which once filed large numbers of lawsuits against users of smart cards.
Spamigation lawsuits are evidently rather inexpensive to conduct, which results in one source claiming that the RIAA actually makes more money from settlements in these cases than it costs to file the lawsuits. Because of the costs of mounting a legal defense, almost all defendants in these cases tend to settle. The RIAA then uses the money from these settlements to "file more suits."
In Brad Templeton's original message post about spamigation, he said:
Spamigation is similar to a strategic lawsuit against public participation ("SLAPP"), which is filed by a large organization, or in some cases an individual plaintiff, to intimidate and silence a less powerful critic by so severely burdening them with the cost of a legal defense that they abandon their criticism. Spamigation differs in that it aims at stopping an economic activity, in the case of the RIAA's lawsuits the copying of copyrighted material.