'Generation' in the Bible

Yahweh said to Jehu, "Because you have done well in executing that which is right in my eyes, [and] have done to the house of Ahab according to all that was in my heart, your sons of the fourth generation shall sit on the throne of Israel."

This was the word of Yahweh which he spoke to Jehu, saying, "Your sons to the fourth generation shall sit on the throne of Israel." So it came to pass.