What are "chatter marks"--and how does one, first, recognize them, and, second, have any idea about what they may show about the age of a building?

I went to a wedding yesterday, and heard a student of architecture talking about "chatter marks" on a building that let him know which part of the building had been built c. 1770, and which parts hadn't. I never did recognize the chatter marks because I didn't know what I was supposed to be looking for!

Thanks for any information.

Best regards,
WW