Soap on a rope is a bar of toilet

soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used ...

that is molded around a small loop of rope. The user is meant to place the rope loop over their wrist. Soap on a rope was invented in the late 1940s after soap makers realized they could mold soap around any object.

References

Novelty items Cleaning products Year of introduction missing Soaps {{product-stub