What does STBL stand for?

Stable

 Incapable of spontaneous radioactive decay. Ability to resist collapse and deformation; stability characteristic of a structure that is able to carry a realistic loadwithout collapsing or deforming significantly. Pertaining to a confirmed state of position without change. Stable a system characteristic in which the transients all decay to zero in finite time is said to be stable. If any transient term grows with time, then the system is unsta-ble. If the transient persists, then the system is marginally stable.