A variation of a card, can be different color border or foil etc...Here's an example with 2013 Bowman Football:link
Lists color variations and others and if they are numbered and to what. Too many parallels as they have taken the concept and have beat it to death. As a player collector I don't need 15 different variations of the same card to chase, but to each their own.
Difference in Hobby and Retail varies on the products, sometimes it is just different inserts or things that are not in the other, other times they use a totally different card stock so the Retail version is on thinner cardboard and less fancy paper (no foil for example).
Also there is a "Ask The Experts" section on board that would be a good place to search topics to learn some things and if you can't find anything then post a topic there with your questions.