From HelpWiki

SS stands for side saddle. This is a type of riding where both legs are to one side of the saddle instead of one leg on either side of the horse. Believe it or not, you can also jump side saddle. If your horse has talent as a side saddle horse then it will have excellent odds on the show entries page.

On WOSE, Side Saddle event includes the classes:
Side Saddle
Side Saddle II
Side Saddle Equitation
Side Saddle Over Fences
Side Saddle - Dressage Routine

Do not confuse Side Saddle Equitation with that of the regular Equitation (or EQ) class.  A Side Saddle horse will only have high odds in the Equitation class instead of excellent.  Also, the Over Fences class should not be confused with Show Jumping, Eventing, or Cross Country classes.

If your horse has excellent odds in Side Saddle, it can go into any Side Saddle class and still have excellent odds.

History of Side Saddle

This started in....

Side Saddle in the Real World

And I would put something here...