Skepticism is using critical thinking and the scientific method to examine the validity of claims. Skeptics practice critical thinking, reject logical fallacies and recognize that lazy thinking is faulty thinking. Most of all, skeptics question their own beliefs because no one is above being sucked into believing a false idea.
Some of skeptics favorite topics of scrutiny include:
Paranormal claims like esp and psychic phenomena
Cryptozoology such as Big Foot or the Loch Ness Monster,
New Age claims of magical thinking such as The Secret
Misuses of scientific ideas such quantum theory, energy or the theory of realitivity,
Alternative health practices with little or no scientific support like homeopathy, reiki, or the latest diet craze,
Conspiracy theories like chem trails or alternative theories about 911,
Urban legends and myths
Any other extraordinary claims, like free energy machines or the latest email chain mail hoax
Finally, skeptics would rather believe what is true than believing in what makes them comfortable.
Dr. Paul Kurtz succinctly describes the type of skepticism The Cleveland Skeptics aims to promote:
"Skepticism is a perspective that does not accept or reject claims at face value, but withholds judgment until sufficient evidence is available to make a decision." -Eugenie Scott
"Modern skepticism is embodied in the scientific method, which involves gathering data to test natural explanations for natural phenomenon. A claim becomes factual when it is confirmed to such an extent that it would be reasonable to offer temporary agreement. But all facts in science are provisional and subject to challenge, and therefore skepticism is a method leading to provisional conclusions.
A skeptic is one who questions the validity of a particular claim by calling for evidence to prove or disprove it." -Michael Shermer
"A skeptic is one who prefers beliefs and conclusions that are reliable and valid to ones that are comforting or convenient, and therefore rigorously and openly applies the methods of science and reason to all empirical claims, especially their own. A skeptic provisionally proportions acceptance of any claim to valid logic and a fair and thorough assessment of available evidence, and studies the pitfalls of human reason and the mechanisms of deception so as to avoid being deceived by others or themselves. Skepticism values method over any particular conclusion." -Steve Novella
"...It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." -Carl Sagan