What is the part called from the dishwasher that the overflow comes out of on your sink

Assuming you are speaking of that round thing on your sink flange, about 1 1/2" diameter and 2" high, usually chrome colored. It is called an air gap. Water is pumped up from the dishwasher to the air gap. The water then flows back down another pipe to your disposal or sink drain. This prevents dirty water from your sink drain entering your dishwasher.

Why do you ask?

Air gap