In architecture, the façade of a building is often the most important from a design standpoint, as it sets the tone for the rest of the building. Many façades are historic, and local zoning regulations or other codes greatly restrict or even forbid their alteration.
On a movie set, many of the buildings are only façades, which is far cheaper than actual buildings, and not subject to building codes. These are simply held up with supports from behind, and sometimes have boxes for actors and actresses to step in an out of from the front if necessary for a scene.
"Façade" is sometimes used as a figure of speech as well, to describe the "face" that people show other people. An example of this might be a person who seems very professional and organised on the outside, but is really feeling very disorganised and stresseded on the inside.