This is a national referendum or vote. In usage, it seems to refer to direct votes (not representative votes) associated with national determination – for example, to vote whether to secede from or merge with another country.
Some people have referred to the 2016 “Brexit” vote as a plebiscite. In that situation, the United Kingdom had a direct nationwide vote on whether or not to leave the European Union. Technically, the vote was a “referendum,” but the line between two concepts is vague – one definition I saw said that a plebiscite is a “referendum specifically dealing with national sovereignty.” Of course, Brexit wasn’t technically about national sovereignty, just continued membership in an economic treaty.
From the Latin “plebis scitum” which means, literally, “the law of the common people.” In Ancient Rome, the “plebs” or “Plebeians” where the average citizens of Rome – not slaves or servants, but not noblemen (“Patricians”) either.