My first thought is it’s a floor drain until I notice it is close to the wall.
This is a location for a clean out. Can you see standing water?
If it is a clean out and not a floor drain it should not be left open.
If you see standing water indicating a p trap below the floor it is a standard floor drain and would be fine to continue to use for the ...
This is a regular basement floor drain. there is a trap below the slab and that's why you see the water... that's a good sign. You should get a drain cover from your home store similar to the one below. Measure the diameter of the drain and hit the home store or a plumbing supply store for the cover.
It's just a typical floor drain, and it's the ideal place to drain your dehumidifier. What you see is the water trap, which prevents sewer gas from escaping. It presumably connects to your sanitary sewer, so be conscientious about what you dump into it.
Here's a modern drain just to illustrate the trap concept: