The scientific and atheistic communities toss around the word "pseudoscience" a lot and I think the word is problematic. I never use it. In this essay I'll explain why. The vague concept of the term means something that resembles science but is not. In practice, I find it gets used in the following ways:
Pseudoscience as bad science Sometimes people will call a field pseudoscientific if the people doing the research did not use good scientific methodology. For example, as reported in the incredibly terrible movie What the Bleep Do We Know? http://en.wikipedia.org/wiki/What_the_Bleep_Do_We_Know!%3F
If you watch this movie, please don't pay to do so. It's an irresponsible movie that should never have been made.*
There is "research" reported that putting negative vs. positive emotion words on glasses of water affect the beauty of the shapes of crystals formed in the glasses. You can see some of these pictures at
Which, interestingly, was research conducted by a guy named "Emoto:" http://en.wikipedia.org/wiki/Masaru_Emoto
"In the day-to-day work of his group, the creativity of the photographers rather than the rigor of the experiment is an explicit policy of Emoto. Emoto freely acknowledges that he is not a scientist, and that photographers are instructed to select the most pleasing photographs."
For this experiment to be conducted appropriately, you'd need to get a random, representative sample of photographs from each glass of water, and have them rated for their aesthetic beauty by raters who did not know which glasses they came from. So what is unscientific about this? Well, he screwed it up. He used bad methodology. Scientists (should) know better. We can call it pseudoscience, but I think "bad science" is more accurate.
Pseudoscience as religion
Sometimes a religion will be called a pseudoscience, or, more commonly, some suite of beliefs from religion. Creationism, and it's reboot title "intelligent design" get this all the time. To me, religion resembles science so little that I think the term pseudoscience is inappropriate.
Creationism, on the other hand, I think is more appropriately called bad science or bad theory.
Pseudoscience as bad theory
Sometimes fields are called pseudoscientific because the underlying theory is perceived to be obviously incorrect. Examples include astrology, creationism, and psychic ability. I think this is an unfair use of the "pseudoscience." I say this because you can do good scientific research and still get poor results. We test theories all the time that don't work out. We publish them. That's great. It's good science. Now, if you're doing parapsychological research and you are doing the science well, I think it's unfair to say what you're doing is pseudoscience. It's also unfair to call it pseudoscience purely because of the topic. That is, labeling all parapsychological research as pseudoscience just because it wants to test some telepathy theory is not fair.
The prevailing scientific view of parapsychology is that it's been tested so many times that we are very sure it's not real. Thus, further research is unwarrented. And maybe it is. But that doesn't mean the science was done incorrectly. Let's say you did a telepathy experiment that came out with negative results. That is, you found no evidence of telepathy. Further, let's say you did everything right. I don't think anyone would say it's bad science. No, they'd say, it's science. Now let's imagine you do a telepathy experiment but screw it up, and the results are positive. Let's say you do it Emoto-style. You used flawed methodology and got positive results that superficially look like you've found evidence for telepathy. Then it's bad science. Now let's imagine that you do a telepathy experiment, conducted it well, and came out with positive results. This actually happens, but (according to the scientific consensus) the effects are small and not replicable. This is a problematic case. I would say that it's still irrational to believe in telepathy, but I can't knock the science. I think it's unfair to call such an experiment pseudoscience.
Another wrinkle on this issue is falsifiability. Many say that theories that are not falsifiable are unscientific. I have written on this topic before: http://jimdavies.blogspot.com/2007/06/falsifiability-and-importance-of-theory.html
The problem with this that it's hard to tell a pseudoscience from a protoscience, which might be on its way to being an actual scientific discipline. Also, certain scientific approaches (research programs) are both scientific and unfalsifiable (e.g. behaviorism and perhaps even evolution). The philosophical problem of determining what is science and what is not is called the demarcation problem.
Pseudoscience is only appropriately used for bad scientific methodology, and then is better described as bad science. I don't think the term should be used. In every case it's either inaccurate of unfair.
* I am a firm believer in human rights, and would never say it should be illegal for this film to be made. To me it's a matter of ethics, not law. Like mean comments, you have a legal right to express them, but a moral obligation not to.
Pictured is water, which needs no emotion to be very beautiful.