In case of onlay cast restoration, what does “ shoeing” refer to?
Capping

It refers to the complete coverage of the cusp / cusps of a tooth with sufficient extension of the bevel onto the buccal and lingual surfaces of the tooth.

Shoeing

Refers to a veneer coverage of the cusp of a tooth with only slight finishing bevel on the crest of the cusp.
The bevel is established either at right angle to the long axis of the tooth or in a slight reverse direction.

MDS Prep Bytes (Cast Restoration – Onlay)
Complete coverage of cusps with slight finishing bevel on the crest  of the cusp
Veneer coverage of cusp with slight finishing bevel on the crest  of the cusp
Veneer coverage of cusp with extension of bevel onto facial surface
Complete coverage of cusps with extension of bevel onto facial surface