I don't think there really is a popular definition for capitalism. People who use the word always use it to mean what they want it to mean, usually in the context of praising or criticizing capitalist society.
The best definition (in my ever humble opinion) is that capitalism is a society where the means of production live in a free market, which is completely consistent with what the GP said.
I believe that the common definition in most folks' minds is that capitalism refers to the system we have today in the USA, where the government rewards business interests with handouts, protective regulations, and the like.
This is not capitalism, though. What people are experiencing and objecting to is corporatism [1].
I believe that if people would give real capitalism a chance, the result would be positive. But as it stands now, the economics are too intertwined with the politics. In order to successfully implement real capitalism, the power that the state wields to erect regulations that can be subverted would have to be stripped: we'd have to neuter the government. Clearly the government would never allow that to happen.
It can be argued that as soon as capital begins to concentrate, the benefactors begin to affect policy making to their advantage. Thus you end up with the current system.
Just as attempts at establishing communism end up with coercion and purges of dissent, theoretical capitalism ends up with powerful interest groups in practice.
The best definition (in my ever humble opinion) is that capitalism is a society where the means of production live in a free market, which is completely consistent with what the GP said.