洗濯板
A washboard is a tool designed for hand washing clothing. The use of washboards have fallen out of use in the developed world, where [[washing_machine|washing machines]] have become common. For the developing world, washboards may still be a common sight. In some parts of the United States washboards are used as a musical instrument.

A washboard works by rubbing wet clothing against its corrugated or ridged side.  This helps to remove dirt from the clothing through abrasion.  If soap is used, the rubbing action helps to drive soap through the clothing and allows the soap to carry dirt away.
washboard