Western saddles are often described as having full, semi or quarter bars. This refers to the angle of the saddle tree, which affects the width of the saddle, and thus the fit. A "Full Quarter Horse" saddle fits a horse with a wide, flat back, which is typical of "bulldog" Quarter Horses. Like this guy.
Regular bars are even narrower. So it goes Regular, Quarter Horse, Semi Quarter Horse and Full Quarter Horse. (Which often fit draft horses too). English saddlers don't use the terminology.