Ritter was a hereditary title derived from the imperial knights (
Reichsritter) of the Holy Roman Empire, who held land directly from the emperor and originally owed military service in exchange. The title is usually translated as "baron" in English, although that's not an exact match (there were barons in Germany and Austria as well).
Captain von Trapp, for instance -- best known as the father in
The Sound of Music -- was a
Ritter. When the Holy Roman Empire was dissolved in 1804, I believe the Austrian emperor maintained the right to bestow the title
Ritter on his subjects, but I'm not sure if he ever exercised it.
To be a
Ritter in the nineteenth century, then, meant that the bearer of the title was of the lower nobility and frequently a member of a very old family, which leant the title the sort of prestige that some newer noble creations lacked.