In the United States, Independence Day (commonly known as the “Fourth of July,” “July Fourth”, the “Glorious Fourth”, or simply the “Fourth”) is a federal holiday commemorating the adoption of the Declaration of Independence on July 4, 1776, declaring independence from the Kingdom of Great Britain.

Independence Day is commonly associated with fireworks, parades, barbecues, picnics, baseball games, and various other public and private events celebrating the history, government, and traditions of the United States. Fireworks have been associated with the Fourth of July since 1777.

[edit] Why the fourth?
Though the Fourth of July is iconic to Americans, some claim the date itself is somewhat arbitrary. New Englanders had been fighting Britain since April 1775. The first motion in the Continental Congress for independence was made on June 4, 1776. After hard debate, the Congress voted unanimously, but secretly, for independence from Great Britain on July 2 (the Lee Resolution) and appointed Thomas Jefferson to write a draft. The Congress reworked the draft until a little after eleven o’clock, July 4, when twelve colonies voted for adoption (New York abstained from both votes) and released a copy to the printers signed only by John Hancock, President of the Congress, and Secretary Charles Thomson. Philadelphia celebrated the Declaration with public readings and bonfires on July 8. Not until August 2 would a fair printing be signed by the members of the Congress, but even that was kept secret to protect the members from possible British reprisals.

John Adams, credited by Thomas Jefferson as the unofficial, tireless whip of the independence-minded, wrote to his wife Abigail on July 3, 1776:

The second day of July, 1776, will be the most memorable epoch in the history of America. I am apt to believe that it will be celebrated by succeeding generations as the great anniversary festival. It ought to be commemorated as the day of deliverance, by solemn acts of devotion to God Almighty. It ought to be solemnized with pomp and parade, with shows, games, sports, guns, bells, bonfires, and illuminations, from one end of this continent to the other, from this time forward forever more.
Adams was off by two days, however. Certainly, the vote on July 2 was the decisive act. But July 4 is the date that Jefferson's stirring prose, as edited by the Congress, was officially adopted and was the first day Philadelphians heard any concrete news of independence from the Continental Congress, as opposed to rumors in the street about secret votes.