Most generally: "A socio-economic system based on private ownership of resources or capital."
https://en.wiktionary.org/wiki/capitalism#English
As for the unfairness:
Capital accumulates capital, debt accumulates debt. When you accumulate capital, you can own resources (land). This means those with capital will accumulate power.
You can talk about being "bad at capitalism" but the implies you assume everyone starts with equal opportunity (capital, land, power).