Sophism (gr.sophistes meaning "wise-ist," or one who 'does' wisdom, i.e. who makes a business out of wisdom; cf. sophós, "wise man", cf. also wizard) was originally a term for the techniques taught by a highly respected group of philosophy and rhetoric teachers in ancient Greece.
Today, a sophism generally refers to a particularly confusing, illogical and/or insincere argument used by someone to make a point (for example, the "Chewbacca defense"). Sophistry refers to the practice of using such arguments, and is used as derogative for rhetoric that is designed to appeal to the listener on grounds other than the strict logical cogency of the statements being made.
The Sophists are known today only through the writings of their opponents (specifically Plato and Aristotle), which makes it difficult to formulate a complete view of the Sophists' beliefs. However, modern research has shown that their views were much more complex than Plato's depiction.