A state of freedom in all relationships, trade, and property wherein one is free to use ones property to prosper.
Capitalism stems from the Latin word capta, meaning “head”, referring to the mind.
“When I say ‘capitalism,’ I mean a full, pure, uncontrolled, unregulated laissez-faire capitalism — with a separation of state and economics, in the same way and for the same reasons as the separation of state and church.”
-- Ayn Rand
This word has been historically used very differently by the left, marxists, communists, and many others. In fact they use the term to specifically describe what those ideologies stand against using those alternate definitions. Here are some examples:
"Capitalism is an economic system based on the private ownership of the means of production and their operation for profit." -Merriam-Webster
"Capitalism is a widely adopted economic system in which there is private ownership of the means of production." -Britannica.com
You'll note their specific usage of words directly from the marxist definition and used by communists and socialists.
"Capitalism is an economic system in which private individuals or businesses own capital goods." -Investopedia.com
"Capitalism is the social system based on the individual’s right to life, liberty, and the pursuit of happiness." -Capitalism.org
You'll note that as defined this term is almost a disctinction without a difference for anarchism. Which is why it is used in anarcho-capitalism primarily for the purposes of distinguishing that term from the marxists and other older self-contradictory forms of "anarchism".