Communism is when everyone has the same pay (wealth) and social class. It is where the wealth would be split amongst each other and is derived from the word common. No matter what your occupation is you will still make the same amount as everybody else.
This may seem unfair to those who work harder and deserve more money but communism tends to be for the people who need the money. This way wealth is equal amongst all people meaning that everyone is on the same level when it comes to their class. There are no more high classed people hogging all the money while all the lower class people are doing all the work. Karl Marx believed that history was a struggle between classes.
The way things were running at the time was Capitalism which he found really unfair due to the fact that workers would work hard in factories but the owners of the factory would hold most of the money. The owners in this came would be considered the "bad guys" while the hard working people were "good guys." He thought that they should rebel against this system so they can finally be free from the owners of the factories that steal their hard earned money. He had believed communism to be the type of government where the commons or the workers would be in control.