Selle Italia SLR TT, is one of the best selling saddles. TT doesn't mean "time trial" in this case, but Titanium Tubular. The shape and padding are the same as with the standard SLR. The titanium rails make this saddle is one of the lightest available today.
This saddle has a flat rear part, making it highly suitable for riders who remain stationary on their saddle while they ride and whose hips don’t rock from side to side at all. The flat shape provides more support than a round saddle would for these riders.
This is a semi-flat saddle, meaning that the saddle is flat at the front, and raised a little at the back. The shape makes it particularly suitable for riders with a moderate degree of flexibility in their spine. This has to do with how easily these riders can rotate their pelvis: they might need a little extra support when riding upright, but can manage on their own when riding on the drops.