Phil R. Johnson has recently written an excellent primer on Antinomianism at his blog here. Most Antinomians may not be practical antinomians, but they certainly are theoretical ones. Due to their rejection of the law, they tend towards practical licentiousness or at least the toleration of "respectable sins". As Phil remarks:
... in normal theological discourse the term antinomianism usually refers to theoretical antinomianism. Theoretical antinomians don't necessarily advocate extreme libertinism (or practical antinomianism). In fact, a great many theoretical antinomians are known for their advocacy of holiness. (And conversely, many who adhere to "Holiness doctrine" and various other perfectionist schemes are also theoretical antinomians.)
In totally non-technical terms, antinomianism is simply the view that Christians are not bound by any of the precepts of Moses' law—moral, civil, ceremonial, or otherwise.
It is not so much the licentiousness that makes antinomianism what it is, although we certainly do see these in action, but the rejection of the third use of the Law as a guiding principle. Without the law to tell us what is sin and what is pleasing to God, Christian living is rendered directionless and epistemologically indistinguishable from sin. In such a system, no antinomian can legitimately tell anyone that what they are doing is sin, for "we are under grace, not law". Instead, all such telling becomes mere expression of disapproval without any teeth to it except for the possible lose of a relationship.