Penguins are flightless birds belonging to the 'spheniscidae' family, which mostly breed in the Southern Hemisphere. Though they are usually associated with Antarctica, some species are found near the Equator as well. It is believed that the name 'penguin' originated from the Welsh word 'Pen Gwyn', meaning white head. They are hefty birds with a heavy and robust skeletal system. It's their heavy bone structure that hinders their ability to fly.