There are four main species of Boswellia that produce true frankincense. Resin from each of the four is available in various grades, which depend on the time of harvesting. The resin is then hand-sorted for quality.
The English word frankincense is derived from the Old French expression franc encens, meaning "high-quality incense". The word franc in Old French meant "noble" or "pure".
A popular folk etymology suggests a connection with the Franks (the forefathers of some French and Germans), who reintroduced the spice to Western Europe during the Middle Ages, but the word itself comes from the expression.