Smith in coming up with it viewed it as a system that would pay people based on hours worked so that the rich who sat around getting money off the backs of workers would be punished and the workers would be rewarded.

Marx saw it as a system that dispersed power from the nobles to the merchant class. (With socialism as the next step of expansion)

As a contrast to mercantilism we can say it's a non-protectionist system based on globalization/mass imports and exports.

Really the system never changed, the idea of capitalism was just a rebranding for the wealthy.