The classification begins at the basic level that is simple recall skills and progresses to the perceived highest level of cognitive processing which they believe to be “evaluation.” The various levels have often been depicted as a stairway to reference a progressive climb to a higher level of thinking. Each level becomes more challenging as you move higher.
According to Bloom, each level must be mastered before moving to the next higher level. The categories are ordered from simple to complex and from concrete to abstract. Bloom's Taxonomy classifies thinking according to six cognitive levels of complexity: knowledge, comprehension, application, analysis, synthesis, and evaluation. The word taxonomy simply means classifications or structures.
Bloom's Taxonomy is a classification system developed by educational psychologist Benjamin Bloom to categorize cognitive skills and learning behavior.