Outer shell electrons

Among the multiple electrons belonging to an atom, these are the electrons in the outermost electron shell in terms of energy or space. Outer shell electrons are weakly bound to the nucleus and are easily influenced by external factors. They play an important role when bonding with other atoms.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

原子に属する複数の電子のうち，エネルギーあるいは空間的に外側の電子殻にある電子．外殻電子は原子核との結合が弱く，外部からの影響を受けやすい．ほかの原子と結合する際には重要な役割を果たす．

出典　森北出版「化学辞典（第2版）」化学辞典 第2版について　情報