As far as I know, only Singer made a slant shank machine, so it is very unlikely you have a Viking with a slant needle or shank.
If you will do a google search for a slant shank machine (or long or short shank), you will most likely get an explanation of the different kinds of shanks (some with photos). It's what Donna said with more detail. Also you can search on quiltingboard for the same thing. There have been threads on the vintage sewing machine forum about that subject in the not too distant past.
bkay