Ruby Port is the most extensively produced and widely available style of port wine, and is for many people an introduction to fortified wines in general.
The term 'Ruby' is neither officially nor legally regulated. Until the 1960s, it simply indicated a bulk-produced port. However, the port trade now seems to have reached a consensus on the 'Ruby' style; youthful, powerful and fruit-forward. The red-berry fruit aromas which characterize the style match the bright red color which gave rise to the name 'ruby'.
Unlike Vintage Port, most Ruby Port is a blend of young wines (from multiple vintages), and remains untamed by age. Most producers bulk-age their Ruby Port for two or three years, in tanks of cement or steel, to prevent oxidization and retain the wine's fresh, fruity qualities. Because the wines are filtered (and sometimes pasteurized) before bottling, Ruby Ports do not improve with bottle age. The small compensation for this is that they contain no sediment, so they don't require decanting.
A step up from standard Ruby Port is Reserve Ruby Port, typically aged for three or four years. These wines were once described by producers as 'vintage character' port, but that term was deemed misleading, and was eventually outlawed in favor or 'Reserve Ruby'.