What, exactly, is socialism, and what are the advantages/disavantages of introducing it into the USA?

Elsewhere on Fluther, we had a brief discussion about what socialism really is. This is hopefully a cotinuation of that discussion. Is there more than one definition? If so, is there one on which we can agree? Do we have the beginnings of a socialistic system in the USA, or are we in the process of establishing one? If yes, what will be the advantages and/or the disadvantages of having an “American Socialism?”