Guaranteed respect for human rights, separation of powers among state institutions, freedom of opinion and expression, religious liberty, the general and equal right to vote, and good governance are basic requirements or foundations of modern democracies. Anything that compromises or opposes these are not part of the foundations of democracy.
Democracy is distinct from a monarchy, which is a government ruled by a single entity like a king or queen; from oligarchy, the rule of a few people; from aristocracy, the hereditary rule of the elite; and from theocracy, literally the rule of God, but actually the rule of religious institutions and leaders.
A totalitarian government, in essence, exerts political power based on a single ideology chosen by one or few rulers. Citizens who oppose the ruling party's ideology are not tolerated, and their basic human rights are violated through torture, detention, or even death by execution or genocide.
Authoritarian regimes aim to keeping political power and resources to an elite few, to the detriment of their constituents. These regimes do not necessarily have to follow a certain ideology.
Modern nations such as the United Kingdom, Spain, Belgium, the Netherlands, Luxembourg and the Scandinavian countries, are no less democratic despite having a king or queen as a head of state. This is because their constitutions guarantee democratic rights to its citizens and institutions, while limiting the powers of the monarch.