What does Genesis 10:26 mean?

This verse continues the genealogy of Shem, listing the sons of his great-great-grandson, Joktan. In total, 13 sons are listed. The names of several of these sons became associated with well-known areas in the larger region of the Middle East. This is part of chapter 10's "table of nations," explaining the origin of the ancient world's various people groups. The actual dispersal of these people to their eventual geographic regions, does not seem to occur until chapter 11 at the incident of the Tower of Babel.

Jerah is a Hebrew word meaning "new moon." Later on in history, the moon would become one of the foremost gods worshiped in the region, which seems to be the ancestral homeland of Arabic peoples.