In an absolutist system, the ruler holds all the power whereas in a liberal democracy, the people ultimately hold the power.
In an absolute system, the people have no power unless the ruler chooses to give them some. The ruler has absolute power and there is no one who has the right to overrule him or her. This ruler can be called many different things. Absolute rulers have typically been kings and queens, but they can be called emperors or dictators, or any other name that they choose to use.
In a democracy, by contrast, the power resides with the people. Of course, they do not typically exercise it directly. Instead, they elect people to represent them in the government. However, it is still the people who are in charge. They are the ones who get to pick their leaders and they have the ability to remove those leaders from power. This is very different from an absolutist system.