Woo-woo (or just plain woo) refers to ideas considered irrational or based on extremely flimsy evidence or that appeal to mysterious occult forces or powers. Strong Skeptics are very fond of it.
Here's a dictionary definition of woo-woo:
- adj. concerned with emotions, mysticism, or Spiritualism; other than rational or scientific; mysterious; new agey. Also n., a person who has mystical or new age beliefs.
When used by skeptics, woo-woo is a derogatory and dismissive term used to refer to beliefs one considers nonsense or to a person who holds such beliefs.
Sometimes woo-woo is used by skeptics as a synonym for pseudoscience, true-believer, or quackery. But mostly the term is used for its emotive content and is an emotive synonym for such terms as nonsense, irrational, nutter, nut, or crazy.