The term "Francis Scott Key" refers to a specific person, not a common English word. Here’s an easy explanation:
Francis Scott Key (1779-1843) was an American lawyer and poet. He is best known for writing a poem called "The Defence of Fort McHenry" after he witnessed the British attack on Baltimore during the War of 1812. This poem was later set to music and became the national anthem of the United States, titled "The Star-Spangled Banner."