"Outdoor stairs" refers to a set of steps or stairs that are located outside, usually leading up or down to a different level or area outside a building or structure. Full definition
A passenger told the television channel that passengers had to exit the plane using outdoor stairs. (fortune.com)
I lived in Inwood when I bought it, and because it's hilly there are lots of outdoor stairs, so I started deliberately taking those to bump my stair count higher. (policygenius.com)