Here is a quote from http://www.budgieplace.com/basic.html
Most people, at least in the United States, know them as "parakeets." But their real name is "budgerigar." The word comes from the aborigines of Australia, the parakeet homeland. The term "budgerigar" is often shortened to "budgie." "Budgerigar" (or "budgie") is a more specific name than "parakeet," because parakeets are a large group of small parrots, including ringneck parakeets, Quaker parakeets, monk parakeets, etc.