It has thousands of forms, from pure to regulated, and is an umbrella term for many different types of democracy, including republic as a sort of intersecting system. A republic tends to have a relatively similar definition to representative democracy, though regulations against abuse of power and wide decisions that discriminate against the minority very much do exist. Democracy is not a liberty killer, with regulations against itself, it works perfectly fine with the presupposed liberty. NATO is a group of big nations who merely support one another militarily in a confederacy-style system.
Democracy means majority rule. Whatever the majority says, goes. The reason I don't believe in democracy is because government should be confined to maintaining a military, a police, and courts to punish criminals and protect property, and the people will often vote for more than that minimum. I am a minarchist, and democracy allows for unlimited government expansion.