Whether you are buffing out a car, a floor, some metal parts, a countertop or even the finish on a guitar...the verb "buff" derives from the obsolete English word buffe, from the French word for buffalo.
When buffalo were abundant in the 19th century, buffalo hide was used for polishing metal to a high gloss. Soon, any sort of soft leather used for polishing was coined as a "buff", which then inspired the verb "to buff".
