A Band and Loop space maintainer is best described as:

A band and loop space maintainer consists of a metal band cemented on an adjacent tooth (typically the first permanent molar) with a soldered loop of wire extending across the edentulous space to maintain arch length. It is fixed (cemented, not removable by the patient) and unilateral (maintains space on one side of the arch only). It is used after premature loss of primary posterior teeth on one side to prevent mesial drift of the permanent first molar. For bilateral space maintenance, a Nance appliance or lower lingual holding arch (LLHA) would be used.