Surplus value is the value that is being created by the action of human labour. For surplus value to be created, one needs to perform socially necessary labour.
In class society, surplus value is appropriated in part or in whole by the exploitative class (see social class). In capitalist society, this translates into a business' profits.
While in capitalist society, surplus value is somewhat approximate to value-added, it is an entirely different concept.
The goal of a communist society is to be classless, which means there is no one to appropriate surplus value from anyone else. This means everyone owns the full produce of their labour.