The variable identifies the political regime of a country using the Regimes of the World classification by political scientists Anna Lührmann, Marcus Tannenberg and Staffan Lindberg. It distinguishes between closed autocracies (score 1), electoral autocracies (score 2), electoral democracies (score 3), and liberal democracies (score 4). Note that in the source the scale was 0-3 instead of 1-4.
Source: Our World in Data