(covers information from several alternate timelines)
A bathroom, also known as a restroom, waste extraction, or toilet facility, is a room that generally contains a toilet, and may also contain any of the following: sink, shower/sonic shower or a bath tub. These fixtures are then connected to a sewage and waste reclamation system where they are recycled.
In 2255 of an alternate reality, Leonard McCoy sought shelter in the shuttle Bardeen's windowless bathroom in response to his aviophobia. An officer later escorted McCoy, despite his protestations, to a seat. (Star Trek)
In 2364, a series of malfunctions aboard the USS Enterprise-D – which were caused by a microbrain from Velara III – included locking two crew members in the head programmers' restroom. (TNG: "Home Soil")