Abstract thinking is a high-level thought process. Someone who is thinking abstractly is considering a concept in a broad, general and non-specific way. Abstract thinking is the opposite of concrete thinking.
Depth of Thought
Abstract thinking considers not just specific objects (for example, a robin), but broad concepts (such as birds in general). When looking at an abstract painting, for instance, the viewer creates within his mind a concept of what the painting is about.
Specificity of Thought
Ideas that are broad in scope can be thought of generally, rather than specifically. Instead of just contemplating one cat, the abstract thinker will think about the nature of cats, their habits, preferences, and characteristics.
Facts vs. Multiple Meanings
Concrete thinking is mainly interested in the facts, such as the fact that a cat is a black cat. Examples of abstract thinking might include types of black cats, that black cats are considered unlucky by some people, that the ancient Egyptians revered cats and created black statues of a cat goddess.
Happiness, freedom, weather, and wealth are all examples of abstract nouns. They are broad concepts with a variety of definitions, possible interpretations and permutations that can all be considered through abstract thinking.