The document describes the SOLO (Structure of the Observed Learning Outcome) taxonomy, which categorizes levels of thinking into five categories: prestructural, unistructural, multistructural, relational, and extended abstract. Each category is defined by the type and complexity of thinking involved. For example, unistructural involves a single idea, multistructural combines multiple ideas, and relational links ideas together with comparisons and explanations. The document provides examples to illustrate the differences between the categories.