This is a nick name given to a Gibson P-90 Single coil pickup. The cream cover looked like a bar of soap. This style of pickup can be seen on the first production of Les Paul Guitars. The soapbar pickups can be seen on Les Pauls made from 1952 to late 1956 and on Re-issue model thereafter.

These pickups are mounted to the solid body guitar by two wood screws that are located between the A & D and the G & B poles.