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.
Why I Looked It Up
From a book about World War 1:
[The Germans] were willing to renounce German sovereign rights to Alsace-Lorraine, but wanted a plebiscite to be held there.
The Germans had taken Alsace-Lorraine from France in the 1870s. When Germany was defeated in in 1918, France wanted it back. The Germans wanted the population of Alsace-Lorraine – which was mostly German-speaking – to decide if they wanted to be part of Germany or France.
I can’t tell if the desired plebiscite ever took place, but France got the territory back and deported more than 100,000 Germans who settled there since 1870 back to Germany. The Germans would control the territory again during World War 2. It is currently part of France.