In 1966, U.K. Fender distributors received a custom run of 20-30 Precision Bass guitars with non-contoured bodies; most of these had another unusual feature in the form of a black pickguard. Those who got them included Ace Kefford (the Move), Clive Taylor (Amen Corner), Steve Currie (T. Rex) and, most prominently, Who bassist John Entwistle, who was known to prefer these models and acquired three of them (“I don’t know what they used on them but those basses had a sound of their own; really raunchy with more of a growl than a regular Precision,” he told Bassist magazine in 1995). These rare British Fender Precisions are better known by what term that refers to their “non-contoured” body style?
Updated with answer: “Slab” body Precisions
Entwistle in 1966 with an Olympic White slab-body custom Precision.