A pop-up sink drain is a common type of drain used in many homes. The reason they are called "pop-up" drains is because they have a small, round cap that pops up when you need to use the drain. To use the drain, simply push down on the cap and it will open up. Then, when you are finished using the sink, push the cap back up and it will close off the drain.
Pop-up sink drains are a great option for many people because they are easy to use and they do not require any special tools or skills to install. However, there are some downsides to using a pop-up sink drain. One downside is that if your sink does not have an overflow hole, then water can come out of the top of the pop-up drain when you are using it. This can be annoying and messy. Another downside is that if something gets caught in the pop-up mechanism, it can be difficult to remove without damaging the mechanism.