1.
framework; skeleton; structural frame
The basic structure or frame that supports something, such as a building, ship, or conceptual plan.
2.
outline; basic structure (figurative)
The basic framework or outline of a plan, story, or concept.
Compound of 骨 (bone) + 組み (assembly). Refers to the essential supporting structure — both literally (buildings, ships) and figuratively (plans, stories).