Soap Scum is that hard to clean film that clings to bathtubs and sinks. It can be found in other places but these two places are the most common. The minerals in water, especially hard water, create soap scum when they mix with soap. It will build up in the tub, tub walls, and will coat the fixtures of the tub or shower.
Hard water can be corrected by using water softeners. These remove many of the minerals that are in hard water. Water softeners will remove the calcium and magnesium that is present in hard water. If your soap doesn't seem to lather as well as it might hard water might be the problem.
Soap scum isn't too bad when there is a thin layer, but if you let it go it can be very difficult to clean. Nobody wants to clean the bathtub right after a bath or shower, but an every few days or once a week cleaning schedule can make cleaning soap scum easier.
There are a few things that are found in most homes that can be used as a general soap scum cleaner. These items include Baking soda, Lemon oil, borax, and ammonia. Borax and Baking soda are abrasive cleaners. Lemon oil will not only clean but coat the surfaces to help prevent future buildup. Ammonia is an extremely harsh cleaner and should be used with caution.
There are also plenty of commercially available cleaners. Most should be sprayed on and let to sit for a few minutes before being wiped or scrubbed off. They all claim to be the best so pick your favorite and have at that soap scum.
As with most other household cleaning problems, frequent upkeep will make the chores a lot easier. Life tends to get in the way, and those chores get pushed down the list of things to do. But now at least you know what soap scum is when you're cursing it.