> What is it then?
I'd say it's a property of forms of government, or of constitutions: some of them are more democratic than others. Sometimes it's obvious which of two systems is more democratic; sometimes reasonable people will disagree. There can be different opinions on which criteria are most important. For example, how much does it matter if convicts are not allowed to vote, or if homeless people find it almost impossible to vote in practice? But also it's not really the formal rules that matter. How things work in practice can be more important. How are the rules interpreted? Do people really follow them? What would happen if the government broke the rules? How would people behave in a crisis?
Like I said, my feeling is that the UK has a relatively strong culture of democracy despite having a very bad electoral system and a monarch that could theoretically refuse to give royal assent. I think a government that was really hated by a big majority of the population would be removed without violence before too long. I think that's how one philosopher (Karl Popper?) defined democracy. But I'd still like to see things improved.