I don't normally use that term, so I could be wrong. Here' what I think it is. The beginning of Chapter 18 is an extended comparison about Jeremiah going to a potters house and noting that when the potter "threw" something he didn't like, he squished the wet clay and started all over again.
Jeremiah says that's the way Jerusalem is. The original pot would be destroyed. In fact further down, it says that God can revoke his agreements if Judah does not shape up.