When a rum states that is is aged, it is referring to the time it has spent inside a wooden (typically oak) cask. In the US, rum has to state the youngest age of the product that went into the bottle, in Europe that same bottle can state the oldest. Some countries also allow casks in the warehouse to be refilled, to reduce the amount of product lost to evaporation, while on the other hand other countries do not allow this practice, resulting in higher loss to evaporation. Climate the rum is aging in also helps determine how the rum is interacting with the cask. Age is not an indication of quality. Having knowledge of the country of origin, that countries laws and the age stated on the bottle are all helpful in determining a rums character.