Keturah
Keturah is a wife taken by Abraham after Sarah's death. The two passages that name her are essentially the same record — one in Genesis, one repeated by the Chronicler — and both are concerned with the line of children she bore to Abraham. Genesis calls her his wife; Chronicles calls her his concubine.
Abraham's Later Wife
The Genesis notice introduces her in a single sentence and then gives the full descent: "And Abraham took another wife, and her name was Keturah. And she bore him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. And Jokshan begot Sheba, and Dedan. And the sons of Dedan were Asshurim, and Letushim, and Leummim. And the sons of Midian: Ephah, and Epher, and Hanoch, and Abida, and Eldaah. All these were the sons of Keturah" (Gen 25:1-4). Six sons are named, and the line is traced for two further generations through Jokshan and Midian.
The Chronicler's Re-Listing
The Chronicler returns to the same list and adjusts the title: "And the sons of Keturah, Abraham's concubine: she bore Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. And the sons of Jokshan: Sheba, and Dedan. And the sons of Midian: Ephah, and Epher, and Hanoch, and Abida, and Eldaah. All these were the sons of Keturah" (1 Chr 1:32-33). Where Genesis had said wife, Chronicles says concubine. The descendants are unchanged. In both passages Keturah's significance is genealogical — she is the mother of a substantial branch of Abraham's offspring distinct from the line of Isaac.