What does the 'and the rockets red glare, the bombs bursting in air' line mean in the Star Spangled Banner?

It was in reference to the battle that was going on as the man who wrote it wrote the song. Through all the bombs and firing, the flag was still flying.|||This song was written when England was trying to re-take the Colonies. It was written after a fierce battle in which the British fired numerous bombardments against Washington DC. It means that our freedom survived through the rockets red glare and the bombs bursting in air.