Critical Thinking is disciplined thinking that is clear, rational, open-minding, and informed by evidence. dictionary.reference.com
Active, persistent and careful consideration of a belief or supposed form of knowledge in light of the grounds that support it, and the further conclusions to which it tends. John Dewey, 1909
The American Philosophical Association has defined critical thinking as "the process of purposeful, self-regulatory judgment. The process gives reasoned consideration to evidence, contexts, conceptualizations, methods, and criteria" (1990).