There can be just a shower, just a bathtub or both; and often both plumbing fixtures are combined in the bathtub.
The room may also contain a sink, often called a "wash basin" or "hand basin" and often a "lavatory".
In the United States, "bathroom" commonly means "a room containing a lavatory".
In other countries this is usually called the "toilet" or alternatively "water closet" (WC), lavatory or "loo".
The word "bathroom" is also used in the U.S. for a public toilet (the more formal U.S. term being "restroom").