Others have already explained the elongation mark, but for those who are interested, there are so many foreign words that have been borrowed into Japanese that

Others have already explained the elongation mark, but for those who are interested, there are so many foreign words that have been borrowed into Japanese that sometimes you get words that differ only in the usage of that elongation mark. ビル: pronounced "biru" is a shortened word meaning building. ビール: pronounced "biiru" means beer.