What is "pagus"

In the later Western Roman Empire, following the reorganization of Diocletian, a pagus (compare French pays, Spanish pago, "a region, terroir") became the smallest administrative district of a province. By that time the word had long been in use with various meanings. Smith's Dictionary says of it, "The meaning of this word cannot be given in precise and absolute terms, partly because we can have no doubt that its significance varied greatly between the earliest and the later times of Roman history, partly because of its application by Latin writers to similar, but not identical, communities outside Italy ..."