What is the general classification or categorization of penguins?

Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless birds living almost exclusively in the Southern Hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have evolved into flippers.

Most penguins feed on krill, fish, squid and other forms of sea life caught while swimming underwater. They spend about half of their lives on land and half in the ocean. Penguins are popular around the world, primarily for their unusually upright, waddling gait and (compared to other birds) lack of fear of humans.