What does 1 Chronicles 3:2 mean?

Absalom, whose mother was Maacah, the daughter of Talmai, king of Geshur; and Adonijah, whose mother was Haggith; 1 Chronicles 3:2 - Modern Text Bible

(The list continues with Absalom and Adonijah, both important figures in later stories about David's family, and notes their mothers' backgrounds.)