Early Bird Special comes from an old American saying ”The early bird gets the worm” which comes from an old English proverb “"The early bird catcheth the worm." Cited in John Ray's A collection of English proverbs 1670, 1678.
The basic meaning is that the earlier you start something the more likely you are to get it.
An “early bird special” refers to deeply discounted meal specials usually offered before an establishments normal busy hours. Anything from 4PM till 6PM give or take an hour on each end. They also often offer two for one cocktails or discounted special drinks.
These are also referred to as Twilight Specials and a myriad of other terms.
One of the biggest groups that patronize these specials are retired senior citizens who can get out earlier than the folks still working and live on fixed incomes. Owners love them for the extra turn, all be it a lower profit margin. Servers hate them because seniors are notoriously poor tippers.
Many chains offer them and even white table cloth restaurants.
On a personal note one of my favorite places, a Chef/Owner establishment called the
West End Café
http://www.westendli.com/index.html has a great one. They call it “Prix Fixe Twilight Menu” Sit down before 6PM and you get an app, entrée and dessert for less than the price of an entrée served after 6. The food is the exact same as the regular menu items. If you’re ever in Nassau County, Long Island NY I recommend it highly.