n. From Latin and Middle English ~ "false science"

A system of theories or assumptions that are erroneously regarded as scientific.

Pseudosciences share the following attributes:

Associates With True Science
Pseudoscience attempts to associate itself with true science, often by founding itself in true science, or confusing its concepts with genuine science. For example Phrenology is based in the concept of the localization of brain functions, which is a real phenomenon, however there is no evidence this carries over to skull morphology.
Relies on Anecdotal Evidence
The reliance on the uncritical acceptance of anecdotal evidence is another key feature of pseudoscience. While there is nothing wrong with accumulating anecdotal evidence to support a theory, a problem develops when one relies exclusively on anecdotes. This is because anecdotes are selective; examples that don't fit are ignored. For example when Arnold Palmer won the British Open in 1962 all three of his biorhythmic cycles were high. Taken alone this supports biorhythm theory, however if you looked at Palmer's entire career it would become evident that there is no correlation between biorhythms and golfing success. In fact biorhythms have been found incapable of predicting accident rates, baseball batting averages, mood swings, performance on tests, and a host of other behaviours (Hines 1979).
Sidesteps Disproof
One of the hallmarks of a good scientific theory is that it can predict specific outcomes and if those outcomes do not occur the theory can be disproved. For example Einstein postulated that time will appear to move slower the closer one gets to the speed of light relative to someone moving at a slower speed. This was supported when an atomic clock was flown aboard an airplane then returned to the ground and checked against another reference atomic clock to find that time dilation had indeed occurred. Had the opposite occurred and the two clocks showed exactly the same time, this would be strong evidence to disprove Einstein's theory. Pseudosciences however avoid disproof by rearranging or adding new bits to their theory. For example if a known pacifist has a large area for destructiveness on his skull, a phrenologist might counter that this is counterbalanced by an even larger area of benevolence, or that he simply represses his destructive tendencies. Thus for pseudoscience any possible outcome can be explained. Yet a theory that explains all possible outcomes fails as a theory because it can never make any specific predictions. Another way disproof is sidestepped is that research reports in pseudoscience are notoriously vague. Real science will be presented with enough precision that replication is possible.
Reduces Complexity to Simplicity
Finally pseudosciences reduce complex phenomena with equally complex causal factors to very simple phenomena with simple causal factors. Your chances of gaining employment at an organisation are based on a complex amalgam of factors. Your perceived skill level, physical attractiveness, temperament, educational background as well as the interviewer's subconscious biases, and the internal politics and corporate environment at the hiring organisation could all come into play. Conversely an astrologer might claim that your chances of being hired are simply a function of the fact that Jupiter is in the third house of Aquarius.

On Hyphenation: Both Webster's International Dictionary and The American Heritage Dictionary agree that "pseudoscience" should not be hyphenated e.g. "pseudo-science". The OED claims that either version is acceptable. Because the OED tries to catalogue all usage, and while hyphenation has been used in the past, I find Webster's and American Heritage more useful in this instance as a guide to modern usage.


Works Cited

Goodwin, James C. Research in Psychology: Methods and Design NY: JW&S, 1999
Hines, T. M. 1979 Biorhythm theory: A critical review. The Skeptical Inquirer, 3, 26-36
"Pseudoscience." Vol XII of The Oxford English Dictionary. 2nd ed. 1989.
"Pseudoscience." American Heritage Dictionary of the English Language. 4th ed. 2000.
"Pseudoscience." Webster's Third New International Dictionary of the English Language Unabridged. 1993.