All the proposed definitions of this concept can be summarized in two groups. In the most common group collected the examples of the meaningless tautology. In general terms, thinking is define as ability or process of mental activity. For example, "Thought is the process of using your mind to consider something." Here is another interesting product of thinking activity: "The thinking - a product of mental activity."
Another group of definitions is thinking as a form of reflection inherent in man.
We see that both groups exhibit the strong anthropic principle. Some authors believe that animals have a "lower form of thinking." However, this does not change matters.
Thinking often presented as a mechanism for obtaining knowledge. This is a general epistemological mistake, because knowledge impossible to transfer or get. Organism can get or transmit information, but it cannot get or transmit knowledge. I will write this later.
V.V. Druginyn and D.S. Kontorov (1981) define thinking as "seeking to reduce uncertainty ...". I took it as the basis of this definition. My edition: "Thinking - the process of reducing the level of uncertainty relations. This definition is pithy, no contradictory and is comprehensive.
The process of thinking can be strong-willed, conditionally reflex and unconditionally reflex. Organisms with neural a system also can be able to think. We know examples of the appropriate behavior of the plants and even bacteria (virulence, carriage of bacilli) depending on changes in environmental conditions.
The apparatus of thinking - is an information mechanism of the organism which can reduce the uncertainty relations. Nature shows the five levels of the hierarchy of systemic organization of information tools. On the human level, these devices operate as a single entity. Consciousness is able to allocate a mechanism which will be priority at the moment. Apparatus of thinking of man has the maximum number of degrees of freedom. This provides the best opportunity for adaptation - anticipatory reflection. This is the main content of process thought.