Whether or not it is the case, I think of the term "rear surround(s)" as being exclusive to 6.1 and 7.1 configurations, and they are mounted on the back wall or corners. The term "surrounds" are found in all 3 configurations and are meant to mounted on the side wall (or, to the sides of the listening area), but CAN be effectively placed on the back wall, or behind the listening area. If someone is talking about a 5.1 configuration and uses the term "rear surround(s)," it is only confusing the issue.
Just my opinion.
"People generally quarrel because they cannot argue." - G. K. Chesterton