In practical terms, a democracy is different from other forms of government, like a monarchy. A democracy involves citizens having the ability to pick their representatives. This is different than a monarchy, which consists of a dynasty (family) where power is passed down from one generation to the next. A democracy is also different from an autocracy, in which one leader has the ability to make all of the decisions for a country on their own without limits.
Theoretically, a democracy is different from other forms of government like an oligarchy. An oligarchy is a type of government in which power is concentrated in the hands of a few highly intelligent individuals. This is much different than democracy, as almost all citizens play a role in the countries government structure.