A humid hide is a container filled with water and moss or a cloth of some kind, meant to create a humid area for your snake. Depending on the size of your snake it can be something as simple as a cool whip container with a hole cut in the side or lid. It's used mainly during shed if you don't have good humidity in your enclosure. My cousin would always take the hot side hide out and replace it with the humid hide during shed, placing it right on top of the heat pad and under the heat lamp to maximize the humidity in it. I tried doing that but Yuki refused to go in it and simply slithered around for an hour or so until I gave in and gave her her normal hide back. When I put the humid hide in with the hot side hide, she still refused to go in it, but I know my cousin's snake seemed to love her humid hide. Seems kinda hit and miss to me, but I might have just gotten an unusual ball python that simply doesn't like it.