Taxonomy is the science of classifying and categorizing organisms based on their characteristics and evolutionary relationships. The correct sequence of taxonomic categories is phylum-class-order-family-genus-species. This is also known as the hierarchical system of classification.

- Phylum: The highest taxonomic category, phylum, is used to group organisms based on their basic body plan. Organisms within a phylum share certain fundamental characteristics.
- Class: The next category is class, which further divides organisms within a phylum based on additional characteristics.
- Order: The order is a more specific category that groups organisms within a class based on similarities in anatomy, physiology, and behavior.
- Family: The family is a taxonomic category that includes organisms with even more specific similarities. Organisms within a family share common characteristics and are more closely related than those in higher categories.
- Genus: The genus is a more specific category that groups closely related species together. Organisms within a genus share more similarities than those in higher categories.
- Species: The species is the most specific taxonomic category and refers to a group of organisms that can interbreed and produce fertile offspring. Species are the fundamental units of classification and are distinguished from one another by their unique characteristics.

The correct sequence of taxonomic categories, phylum-class-order-family-genus-species, allows scientists to organize and classify the vast diversity of living organisms. It provides a hierarchical framework that reflects the evolutionary relationships between different species. This system of classification helps in understanding the relationships between organisms, identifying new species, and studying the diversity and evolution of life on Earth.