Autocracy is a form of government. In an autocracy, a single person has all legal and political power, and makes all decisions by himself or herself. The person who holds the power is called an autocrat.
When there is a monarch ruling a country as an absolute monarchy, this is also called an autocracy. Having an autocratic government does not mean the country is governed well or governed poorly. It is just a description on how it is set up.
In modern times, most autocrats gain power as part of a larger nationalist, communist, or fascist movement. Once in power, they eliminate all other kinds of authority in the country, such as judges, the legislature, and political parties.