An emergency exit in a structure is a special exit for emergencies such as a fire: the combined use of regular and special exits allows for faster evacuation, while it also provides an alternative if the route to the regular exit is blocked by fire, etc.
The qualifications for an emergency exit are as follows: it must be in a location that is easily accessible, the exit must have an area or location that it can bring people to in the event of any emergency situation, it must be controlled by the inside of the building, it must be well managed and regularly up kept, and it must be in a permanent location.
It is usually in a strategically located (e.g. in a stairwell, hallway, or other likely places) outward opening door with a crash bar on it and with exit signs leading to it. The name is a reference to when they were frequently used, however, a fire exit can also be a main doorway must be able to be unlocked from the inside of the room. A fire escape is a special kind of emergency exit, mounted to the outside of a building.