How is exploitation defined?
Who exploits whom and why?
Eauz's a Marxist definition, but I use the capitalist definition.
When we say exploit something we mean we take advantage of it for selfish reasons - we want to make a profit. Under a savage socialism (aka fascist) model such as has evolved in People's Republic of China, there's very little regulation, so the elites can exploit the working class and the workers have very little recourse. In most democratic capitalist societies, labour laws have emerged to control the selfish nature of the elites who invest.
the For example, let's say I know there's a skilled labor force able to assemble pumps in Indonesia, or one can be trained. I can start a factory and train them, and I can exploit this situation to my advantage making pumps for the local market. The key to induce the selfish investor like me is to allow labour unions to emerge and also pass labour laws which protect worker safety etc. Again, as we saw in the Soviet Union and other communist societies, the fact that the elites are the communists who own the means of production and also control government means they exploit the hell out of the workers, and god forgive any who try to form an independent union. When the communists lost their nerve in Poland and Solidarnosc emerged under Walesa, the communists were doomed - only Soviet troops would have been able to keep the communists in power at the time, and Gorbachov wasn't too keen on using troops after the mess they had in Afghanistan.
I have a message for the communists who post here, based on real life observation, life inside communist systems, and seeing what was left as we dismantled the Soviet Union: Not only was Marx wrong, today he is utterly obsolete as far as modern democracies are concerned.
Marxism never made much sense because it's based on a flawed reading of human nature - Marx and Engels were men who never had to earn a living, and some of their lessons learned about the exploitation of labour were done looking at it from above, as members of the bourguesie or the upper castes. Because they had a limited understanding of the way things work, they didn't realize that the emergence of a monolithic state ruled by a communist elite was the logical end point of their proposed system, and such a powerful elite would then go on to explooit ruthlessly the working class - under communism there's nothing to keep their greed and venality in check. This is why the requisite to take communists out of power is usually the power that flows from the barrel of a gun. Rotten, corrupt communist elites don't go quietly. At best they turn fascists as they did in China and are doing in Cuba.