A fire escape is a type of emergency exit, usually a set of stairs or ladders mounted on the outside of a building and kept separate from its main interior. It gives occupants a way out when a fire or other emergency blocks the inside stairwells. Fire escapes are most common on older multi-story residential buildings, such as apartment buildings.
A typical fire escape has a platform at each floor connected by stairs or ladders, usually made of open steel grating so ice, snow and leaves do not build up. The bottom ladder often swings or slides down only when needed, which lets people reach the street during an emergency while keeping intruders off at other times. External fire escapes were widely added in the 1800s and early 1900s but fell out of use in new construction after the 1960s, as building codes shifted to enclosed interior stairwells, smoke detectors and fire sprinklers.
Source: Wikipedia: Fire escape
Image: Fire escape, West 10th Street, Greenwich Village, NYC, by Spencer Means, CC BY-SA 2.0, via Wikimedia Commons.