What does the term 'overproof' denote on a bottle of rum?

The term 'overproof' when used on a bottle of rum specifically denotes that the rum has a higher alcohol by volume (ABV) than standard offerings. Typically, regular rum might have an ABV around 40%, whereas overproof rum can exceed 50% or even go up to 75% ABV. This higher alcohol content is often sought after for cocktails or certain traditional drinks, providing a more intense flavor and potency.

In contrast, aging longer than usual pertains to the maturation process and does not necessarily indicate the alcohol content. Blending with spices refers to flavored rums, which do not inherently relate to the proof. Mixing with fruit juices describes cocktails or mixed drinks, which also do not imply the proof level of the rum itself. Thus, 'overproof' is fundamentally about the elevated alcohol content in the rum.