Several years ago I read a blog whose name I cannot remember. To paraphrase it, a group of educators entered a discussion on the meaning of critical thinking and ended up agreeing to disagree on the meaning. He also stated that he found significant value in the discussion itself.
I have spoken with some colleagues and have found a similar diversity of answers. One strongly asserts that there is "A definition," and any discussion beyond that is pointless. Another believes any question that he presents that involves any question word from Bloom's taxonomy wheel's application, evaluation, analysis or synthesis areas (http://clihome.com/Docs/CM/BloomsWheel.pdf ) must represent critical thinking, regardless of how many times it has been discussed. I believe that both of these people would benefit from a discussion on the meaning of critical thinking. In fact, in twenty years of teaching in a dozen different buildings, I have not encountered a staff that would not benefit from such a debate. Personally, I do not believe that there is a correct definition, but I do agree that any school that is trying to develop critical thinking, must in some way define what is being worked toward.
How to Assess Higher-Order Thinking Skills in Your Classroom by Susan M. Brookhart tackles this debate by defining three aspects of higher-order thinking: the ability to transfer knowledge to novel situations, critical thinking (reasonable, reflective thinking focused on deciding what to believe or do), and problem solving. Admittedly her divisions are not cut in stone; overlap exists. Her identification of what she is looking for is essential to the remainder of the text just as is it to a school district trying to develop higher order thinking.
To me, higher order thinking is any question that involves doing things with knowledge. If it merely is a repetition or restatement, you may be working with important information. After all, if we did not learn to automaticity the alphabet, no one would be reading this page. However, it is the manipulation of information that is the hallmark of higher order thinking. Integrating information from multiple sources to create a new whole, using information in a new way, tearing something apart to evaluate either its components or its whole are all examples of higher order thinking.