noun
one's remaining years; the rest of one's life
Refers to the period of life after a major turning point, such as retirement, recovery from illness, or a life-changing event. Often carries a reflective or serene tone.
彼は退職後、余生を田舎で静かに過ごした。
After retirement, he spent the rest of his life quietly in the countryside.
大病を患った後、彼女は余生を社会奉仕に捧げる
After a serious illness, she decided to devote the rest of her life to community service.
Composed of 余 (surplus, remaining) and 生 (life). The exact historical derivation is uncertain, but the compound has been used in literary Chinese and Japanese to mean 'remaining life'.