
If you look at the front of the dog side on you will see the shoulder which leads down at the chest level to the upper arm.
Return of upper arm is the angle that the upper am attachés to the point of shoulder and where t then places the elbows.
Ideally the angle formed by the shoulder and the upper arm should form close to a right angle where the two parts meat at point of shoulder.
Many dogs will have a short upper arm so that instead of angling back under the dogs body it hangs almost straight down from where it meats the shoulder assembly, other dogs have straight shoulders, and some have both, each gives a too open angle of the two parts thereby restricting the dogs length of stride.