補欠

1. Origins, structure, and basic meaning

• Structure: 補欠 (ほけつ) is a noun for a person designated to replace a regular participant.
• Basic usage: 補欠が出場する makes a reserve player the subject replacing an injured athlete, while 委員の補欠を選ぶ makes a committee alternate the object of selection.

2. Common pitfalls and similar expressions

• Reserve status and actual substitution
  • 補欠 occurs in both sport and a committee setting. It does not itself say that replacement has already occurred; with 選ぶ, it is a status assigned in preparation for a vacancy.