In this video, Randy explains what a pop up drain is. It is a drain that goes in your sink that does not have a handle in between the handles to plug it up. You simply push it down to stop up the sink. Make sure you know if you need to have the over flow capability or not. A grid drain is a drain that you are not able to plug up to hold water. These would be most commonly used in say a bar sink. The water just flows right on through.