Razor strop

A razor strop (or razor strap) is a flexible strip of leather, canvas, denim fabric, balsa wood, or other soft material, used to straighten and polish the blade of a straight razor, a knife, or a woodworking tool like a chisel. In many cases stropping re-aligns parts of the blade edge that have been bent out of alignment. In other cases, especially when abrasive polishing compound is used, stropping may remove a small amount of metal. Stropping can also burnish (i.e. push metal around on) the blade.

The strop may be a hanging strop or a hand-held paddle. Various abrasive compounds may be applied to the strop to aid in polishing the blade while stropping to obtain a mirror-like finish. Common abrasive compounds include: half-micron diamonds, green chromium(III) oxide, white rouge (aluminum oxide), and jeweller's rouge (iron oxide).

Stropping is traditionally associated with straight razors used for shaving, as these are the thinnest blades in everyday use, and therefore require frequent stropping. Kitchen knives may be straightened on a honing steel if less sharpness is acceptable. In principle, any blade may be stropped to polish it. Custom strops are made to hone irregularly-shaped tools, such as chisels or gouges, and nearly any piece of smooth leather or heavy fabric infused with abrasive compound may be used for stropping.

Two points are key to stropping:

...
Wikipedia