More generally it is usually used to mean a social set of rules in which individuals who take risks (with capital) can reap the rewards of those risks paying off, or wear the cost of them failing.
Other definitions frequently include descriptions of capitalism being the amassing of wealth into the hands of the very few, and conspiracy theories about 10 rich men controlling the world. These so called 'definitions' give insight into the muddy thinking of the left, in that they are not definitions at all - they are merely descriptions of what people believe will happen in a capitalistic society.
Frequently also it is used in a derogatory sense, to describe a society in which some people have significantly more wealth (capital) than others. That is, in which there is poverty.
Capitalism is also equated with the slogan 'greed is good'. Capitalism in fact has less to do with greed than it does with choice. If you choose to be greedy, and spend your life amassing wealth, that's fine under a capitalist system. If you choose to work just enough to support your family, and enjoy the rest of your time as leisure, then that's also fine. The collectivist society forces a certain way of life, and certain values on the individual. The capitalist system does not.
Key to capitalism is the notion of being able to trade freely.
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