What does the the slower traffic keep right sign mean?

Well xD Funny I found this question, I actually had to explain this to my Grandmother. The signs means (In my own words) People who drive slow mabye carfully? or just don't like to go fast, or even elderly people. It's practically telling you "if your driving under the speed limit or slower the usual, please keep on the right lane". hope I helped xP.

Yeah u should that's the right thing