Inheritance is the passing of property from one generation to another upon the death of an individual. Say there is a rich billionaire who dies. His/her children will receive billions of dollars without doing a thing. The only reason why they are receiving this money is because they just happened to be the child of a wealthy individual. Now suppose there is a poor person who dies. The children of that person will receive hardly anything, even if they worked just as hard as the children of the rich person.
Some argue that inheritance does not create inequality because some individuals are foolish with their money, and end up losing it all. However, wealthy individuals have access to better education, and therefore are more adept at hoarding wealth.
In this way, rights of inheritance are harmful to society by creating inequality. Marxists wish to abolish all rights of inheritance.