The term "order Chelonia" refers to the taxonomic classification of turtles. This order includes around 300 species of reptiles that are characterized by their hard, bony shells that they use for protection. Other common names for this order include Testudines, turtle, and tortoise. While all of these names refer to the same group of animals, they may emphasize different aspects of the turtles' biology or behavior. For example, "turtle" is often used to describe aquatic species, while "tortoise" may denote terrestrial species with dome-shaped shells. These synonymous terms may be used interchangeably in most contexts, but their use may depend on the specific type of turtle being discussed.