The FLSTSB is a model designation used by Harley-Davidson for one of their motorcycles. In particular, FLSTSB stands for "Softail Cross Bones." Here's a breakdown of the meaning:
"FL" indicates that it belongs to the Harley-Davidson Softail series. Softail motorcycles have a hidden rear suspension system that gives them the appearance of a rigid-frame "hardtail" bike while providing a more comfortable ride.
"ST" stands for "Softail," which is a specific type of frame design employed by Harley-Davidson.
"SB" represents "Cross Bones," which is the specific model name given to this particular variant of the Softail series. The Cross Bones model has distinct styling cues inspired by the bobber motorcycles of the past.
Overall, the FLSTSB, or Softail Cross Bones, refers to a Harley-Davidson motorcycle model that combines the Softail frame design with the unique styling elements of the Cross Bones model.