Shopi is a regional term for the South Slavic people, self-identifying as Bulgarians, Macedonians and Serbs. The areas traditionally inhabited by the Shopi is called Shopluk (Шоплук, Shopluk, srb. Šopluk), a mesoregion, roughly where Bulgaria, Serbia and Macedonia countries meet.
The Shopluk is a mountainous area on the borders of Serbia, Bulgaria and Macedonia, of which boundaries are quite vague, in Serbia the term Šop has always denoted highlanders. Shopluk was used by Bulgarians to refer to these borderlands just like the Carpathians or Carpaty of Slovak, Ukraine and Poland borders. The Bulgarian borderland inhabitants were called Shopi.
The Shopi designation is currently attributed to villagers around Sofia Bulgaria. Bulgarian scholars put Shopi as a subgroup of the Bulgarian ethnos. As with every ethnographic group, the Bulgarian Academy notes, the Shopi in Bulgaria consider themselves the true and most pure of the Bulgarians, just as the mountaineers around Turnovo claim their land as true Bulgaria from time immemorial.
Source: Bulgarian folk costumes photo © Donald Judge; Folk events: http://bnr.bg/en/post/100976265/shoppe-festival-2018-taking-place-in-bulgarias-elin-pelin