Indirect utilitarian by Yeager

Indirect utilitarian What is meant by that?

source: https://mises.org/library/ethics-soc...-leland-yeager

By reading this, I still do not understand what it is. And do not think there's so much about it online.

I know what utilitarianism is, but not the indirect? Trying to understand what Yeager says here (in the link above)