Refers to one's own former wife. Used in casual conversation, often with a slightly informal or personal tone.
I still keep in touch with my ex-wife from time to time.
His ex-wife is a famous actress.
Compound of 元 (former) and 嫁 (wife, bride). The reading よめ for 嫁 is the native Japanese word for 'wife' or 'daughter-in-law'.