Yep, var. is just the abbreviation for variety. It's a taxonomic subdivision below the species level. It's typically used when separate populations of a given species are not distinct enough to be classified as subspecies, but they are distinct enough to be recognized.
Spiraea splendens has two varieties for example, the "typical" variety, Spiraea splendens var. splendens and another variety called Spiraea splendens var. rosea. I assume there's something noticeably different in appearance between those two varieties, but I don't know enough about them to tell you what it might be. Spiraea splendens var. rosea has a very limited distribution in Idaho, so I'd imagine there's an isolated population on some mountain there that has different colored flowers, or growth habit, or something like that.
