'Custom' in the Bible

So I took the evidence of the purchase, both that which was sealed according to the law and custom, and that which was open:

“The command which Jonadab the son of Rechab gave to his sons not to drink wine has been observed [as a custom for more than two hundred years]. To this day they do not drink wine, for they have obeyed their father’s command. But I have repeatedly spoken to you, yet you have not listened to Me.