Hubba
Also known as: hubba ledge
An inclined ledge running down alongside a set of stairs, made to grind and slide downhill.
Extended definition
A hubba is that sloped low wall or ledge that runs beside a staircase. Unlike a flat ledge it goes down on a diagonal, so grinding or sliding it adds speed and commitment. The name comes from Hubba Hideout, the mythical San Francisco spot, and today it's used generically for any ledge of that kind (sometimes "hubba ledge").
Origin / etymology
From Hubba Hideout, a legendary San Francisco spot.