If you don't know what is then it aint broken so don't fix it.

Obviously, the last part of your handle seems correct :-).

Actually, you have just about covered it. It is the subbase of a shower stall. It has had a long evolutionary process, so, can't really say what yours is made from. Its origin began as a metal pan placed in or on a bed of mortar. It has since been made of plastic, fiberglass and now a membrane over a thinset base. Once the pan and material is in place, then the tile or shower stall is placed directly on it for the finished look. The pan will generally have the 1/4" per foot slope built into it along with the drain hole. Can it be repaired? Not really worth the effort. A new installation would be advisable......

Sorry about my rude reply. I think I got overcome by the power of anonymity and didn't have a witty answer to your reasonable question :-(

Thanks for the responses.

I am having the same problem. But most of all I don't know how to remove the metal drain. It is made of steel. please help!

Are you able to see the underside of the pan, or are you trying to remove it from the top?