|Easton's Bible Dictionary|
Incense, the wife of Abraham, whom he married probably after Sarah's death (Genesis 25:1-6), by whom he had six sons, whom he sent away into the east country. Her nationality is unknown. She is styled "Abraham's concubine" (1 Chronicles 1:32). Through the offshoots of the Keturah line Abraham became the "father of many nations."
Int. Standard Bible Encyclopedia
ke-tu'-ra, ke-too'-ra (qeTurah; Chettoura, "incense"): The second wife of Abraham (Genesis 25:1 1 Chronicles 1:32 f). According to the Biblical tradition, he contracted this second marriage after the death of Sarah (compare Genesis 23), and very likely after the marriage of Isaac (compare Genesis 24). It is not improbable that, as some writers have suggested, this change in the life of his son prompted Abraham to remarry in order to overcome the feeling of lonesomeness caused by Isaac's entering the state of matrimony.
1 Chronicles 1:32 (and also Genesis 25:6) shows us that Keturah was not considered to be of the same dignity as Sarah who, indeed, was the mother of the son of promise, and, for obvious reasons, the sons of Abraham's concubines were separated from Isaac. She was the mother of 6 sons representing Arab tribes South and East of Palestine (Genesis 25:1-6), so that through the offspring of Keturah Abraham became "the father of many nations."
Keturah (4 Occurrences)
Genesis 25:1 Abraham took another wife, and her name was Keturah. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)
Genesis 25:4 The sons of Midian: Ephah, Epher, Hanoch, Abida, and Eldaah. All these were the children of Keturah. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)
1 Chronicles 1:32 The sons of Keturah, Abraham's concubine: she bore Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. The sons of Jokshan: Sheba, and Dedan. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)
1 Chronicles 1:33 The sons of Midian: Ephah, and Epher, and Hanoch, and Abida, and Eldaah. All these were the sons of Keturah. (WEB KJV JPS ASV BBE DBY WBS YLT NAS NIV)