The noun BALSA has 2 senses: 1. strong lightweight wood of the balsa tree used especially for floats. 2. forest tree of lowland Central America having a strong very light wood; used for making floats and rafts and in crafts.Familiarity information: BALSA used as a noun is rare.. strong lightweight wood of the balsa tree used especially for floats. 2. forest tree of lowland Central America having a strong very light wood; used for making floats and rafts and in crafts.