What does SS mean in football on defence?

Answer 1

Safety_(American_football_position) (FS or SS) - The safeties are the last line of defense (farthest from the line of scrimmage) and usually help the corners with deep-pass coverage. The strong safety (SS) is usually the larger and stronger of the two, providing extra protection against run plays by standing somewhere between the free safety and the line of scrimmage. The free safety (FS) is usually the smaller and faster of the two, providing variable and extra pass coverage. Traditionally, teams have looked for safeties with reputations as hard hitters. More recently, however, teams have been looking for hybrid safeties who can do both jobs, as in a cover 2 defense, when the strong safety has a greater role to play in coverage. Safeties are also used in a variety of blitzes.

Answer 2

Yes, it stands for Strong Safety