A French letter is a euphemism for a condom. The term originated in the UK, Ireland, Australia, and New Zealand and is considered dated. The origin of the term is not entirely clear, but there are a few theories. One theory is that it comes from the French word "capote," which means "hood" or "cover," and was used to describe condoms made from animal intestines. Another theory is that it comes from the French soldiers in World War I who were known for their sexual promiscuity, and the condoms were associated with them. The term "French letter" is not used in French to refer to a condom.