The curb-cut is a solid (usually concrete) ramp that grades down from the top surface of a sidewalk to the surface of an adjoining street to allow someone in a wheelchair to move onto or off a sidewalk with less difficulty.  It also benefits a pedestrian when using a walker or cane, pushing a stroller or a buggy for babies, pushing or pulling a cart or hand truck, when riding a bicycle, using roller skates, or a skateboard.  Curb cuts have been mandated by legislation in the American with Disabilities Act (ADA) in the USA.  This requirement to have curb cuts present on all sidewalks is an example of legislation that benefits every user of public spaces, even though the law was aimed to support people with disabilities.  The curb-cut effect represents laws and programs designed to benefit vulnerable groups that often end up benefiting all of society.  It further confirms that whenever the walls of exclusion come down, everyone benefits, not just those who have been discriminated against, marginalized or vulnerable.

For further reading:
The Curb-Cut Effect by Angela Glover Blackwell