Oneself; the person in question—often used for emphasis ('the person himself/herself'). Also used as a suffix.
部長自身が説明に来てくれた。
The manager himself came to give an explanation.
この問題は本人自身で解決する必要がある。
This problem needs to be resolved by the person themselves.
彼女は努力の結果を自身の目で確かめた。
She confirmed the results of her efforts with her own eyes.