Albert Barnes Commentary 1 Chronicles 2:18

"And Caleb the son of Hezron begat [children] of Azubah [his] wife, and of Jerioth; and these were her sons: Jesher, and Shobab, and Ardon." — 1 Chronicles 2:18 (ASV)

In the remainder of this chapter, the writer finds little assistance from the earlier Scriptures and must have drawn almost entirely from genealogical sources, accessible to him, which have since perished.

Azubah was Caleb’s wife and Jerioth his concubine. He had children by both, but only Azubah’s children are recorded.