The word biscuit applies to two distinctly different products in American and British English.
In British English it relates to a small and hard, often sweetened, flour-based product, most akin in American English to a cookie. It comes from the Latin word “biscotus”, which means "twice baked". Not surprising that it is referred to by a variety of names as “biscuit” in French, “biscotto” in Italian and “beschuit” in Dutch.
The second cooking of the biscuit, at 90-100ºC, is intended to remove the remaining moisture. The resulting dried and hard biscuit was the perfect easy-to-carry and long-lasting food for sailors. It would stay intact for years as long as it was kept dry.
In American English a biscuit relates to a softer bread product baked only once, somewhat similar to a scone. In Canada, the terms biscuit and cookie are used interchangeably, depending on the region, with biscuits usually referring to 'hard' sweet biscuits (like digestives) and cookies for 'soft' baked goods (like chocolate chip cookies).
Read more in:
A bite of cookie history by Food.ca.
Biscuit in Wikipedia.