This week's winner of the Heresy of the Week award is:
< / applause >
This term itself is a relatively recent one, and was sort of an interesting reaction to Luther's doctrine of justification by faith alone and not works. Just as Luther stated that good works could not save you, antinomianists taught that neither can you be condemned by bad works. Essentially this means that bad works could not force a Christian from grace because they had faith. In reality, this heresy has its roots all the way back, even to certain elements of Gnosticism and Marcionism.
As an interesting side note, this is the roots of the Evangelical Protestant (especially parts of Southern Baptists and the like) principle of "once saved, always saved."
For an interesting write up on this, click here. Bear in mind this article is from the Catholic Encyclopedia, and though an excellent reference, the article is somewhat slanted against Protestantism.