After reading through the collected writeups here, it's clear that many people have very strong feelings when it comes to the connotations of the word democracy, but not necessarily a firm knowledge of the definition of the word democracy. Such a central concept as democracy is bound to have many strong feelings and opinions, many of which have a lot of validity. Every one of these writeups here expresses a valid opinion; however, they each miss out on a few key issues.
Here, I hope to explain why the central idea here is mostly true, but not quite. In fact, the United States is largely a democracy, more so than any other type of government. This was the idea that the original creator of this node, advid, had when he submitted a writeup proposing that the United States is a republic, which is much less true than stating that it is a democracy. He does deserve credit for realizing that it is in fact not a democracy, however. In reality, it is very difficult to apply any other general form of government (communist, socialist, etc.) to describe the United States (and no one feels that they apply anyway), so I'll skip over these and stick to the two in question.
What is a democracy?
The chief characteristic and distinguishing feature of a democracy is rule by omnipotent majority. In a true democracy, the individual or any group of individuals composing a minority have no protection against the unlimited power of a majority. A true democracy is a case of majority-over-man.
What is a republic?
On the other hand, a republic has a very different purpose and an entirely different form of government. The chief characteristic of the republic is the strict control of the majority and all minorities, protecting the powers of the individual above all. This is achieved by having the populous elect representatives to create and enforce laws and decide their fairness In fact, the founding fathers intended the United States to be a republic, framed by a constitution that would restrict it from becoming anything else.
The problem is that both the idea of a democracy and the idea of a republic are ideals, ones that no true government can ever achieve simply because individuals have different ideals than one another. A true republic cannot exist because one representative can never precisely represent his constituents while simultaneously protecting the freedoms of all voices and opinions to be expressed. Meanwhile, a true democracy cannot exist because minorities would never have a voice, and it would quickly descend into infighting, mob rule, and a new governmental form because in a democracy, the simple majority always rules, even if the strong minority is actually correct.
The question is then begged: what on earth is the United States if it is not a democracy and it is not a republic? It is in fact a representative democracy, a different entity entirely. In terms of structure, it is much closer to a republic; in terms of effect, however, it is much closer to a democracy. Since the effect is what is actually turned into law and action, the government is much more like a democracy than a republic.
How is this so? Over time, the legislative and executive body moved from protecting the views of the minority and controlling the majority to simply obeying the wishes of the majority. Rather than debating issues on merit and allowing all voices to be heard, the Republicans and Democrats instead debate on a partisan basis, usually voting strictly along party lines or in whatever direction opinion polls of their constituency tell them. As a result, the majority rules: whatever party received the most votes at the last election in essence runs the country and enacts their policies because they have the support of the majority.
However, this effective democracy works within the structure of a republic. We have a three-pronged system of government and a constitution that does protect freedom of expression. Essentially, the United States is the monkey of democracy in the suit of a republic. People repeatedly complain that the "people aren't really in control;" that is in fact the result of the democratic elements of our government and the statement comes from people who want to see the republic-like elements of it instead.
For a better understanding of this, I strongly recommend a reading of The Federalist Papers, written by by Alexander Hamilton, James Madison and John Jay. These men provide a great understanding of what exactly the government of the United States was intended to be. To supplement this, try watching C-Span or a few political news programs such as CNN's Crossfire. Such programs will show you what exactly the government of the United States has become.
In the rest of this node, one can find a great debate between The Custodian and SharQ, who both do a great job of discussing the political arena of the United States today in comparison with other systems that have a mix of democracy and republic styles of government. Although their discussions are well worth reading, in essence the two are comparing apples and oranges. None of the systems they describe are truly a democracy, nor are any of them truly a republic. Instead, they debate different perspectives on what exactly the governmental system of the United States has evolved into and its impact on the country. It's a great debate and very interesting reading, but it doesn't address the central point of whether the United States is a democracy or not.
In conclusion, I'll restate the central point again: the United States is largely a democracy, more so than any other type of government; however, it is not truly a democracy.