"Old Glory" is a red, white, and blue flag with thirteen alternating red and white stripes, and a blue field with white stars. The earliest explanation for the colors came from Secretary of the Continental Congress, Charles Thompson. He did not explain the flag specifically, but rather the seal of the country:
"The colors of the [stripes of the seal] are those used in the flag of the United States of America; White signifies purity and innocence, Red, hardiness & valour, and Blue, the color of [the upper field of the seal] signifies vigilance, perseverance & justice."
The original flag had thirteen stripes and thirteen stars signifying the original thirteen states. Those states were Connecticut, Delaware, Georgia, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, and Virginia. The thirteen stars, it was written in the first Flag Act, "in a blue field [represent] a new Constellation."
When the states of Kentucky and Vermont entered the union, the flag was changed to have fifteen stars and fifteen stripes. This was the only time a United States flag had more than thirteen stripes, and was the flag flying over Fort McHenry that inspired Francis Scott Key to write "The Star-Spangled Banner" during the War of 1812.
In 1818, another Flag Act took away the two new stripes and the United States flag has had thirteen stripes ever since. A new star has been added for each new state, and there are currently fifty stars. This version of the flag has been in place since 1959, when Hawaii became the fiftieth state.
When a flag is folded by the military, it is folded into a triangle that is symbolic of the tricorner hats worn by American soldiers during the American Revolution. The folded flag should show only the blue field and some white stars.