According to the definition, a coach is "originally a large, usually closed, four-wheeled carriage with two or more horses harnessed as a team, controlled by a coachman and/or one or morepostilions. It had doors in the sides, with generally a front and a back seat inside and, for the driver, a small, usually elevated seat in front called box seator or coach box".
Lisbon has a museum wholly dedicated to them: after ten days of work needed for the transportation of all its “jewels” in the new location, on May 23rd, the Museo Nacional dos Coches, the National Museums of Coaches will open again. Interestingly enough, the opening day coincides with the 110th birthday of the museum. This means that for the whole day visitors will have the chance to enjoy a completely free entrance. The free entrance is also guaranteed for the next day, and other events like special shows of the coaches are in program.
Here you can find the official website; we also add a few photos to understand what the museum is about: