Clear Transform
Reference
Mode
Pose Mode
Menu
Pose ‣ Clear Transform
Hotkey
Alt-G, Alt-R, Alt-S
Once you have transformed some bones, if you want to return to their rest position, just clear their transformations.
Location, Rotation, Scale Alt-G, Alt-R, Alt-S
Clears individual transforms.
All
To clear everything at once.
Reset Unkeyed
Clears the transforms to their keyframe state.
Only Selected
Operate on just the selected or all bones.
Note that in Envelope visualization, Alt-S does not clear the scale, but rather scales the Distance influence area of the selected bones (also available through the Pose ‣ Scale Envelope Distance menu entry, which is only effective in Envelope visualization, even though it is always available…).