The term "homo economicus" means "economic man." This Latin phrase refers to a specific model of humanity that was developed, logically enough, in the field of economics. In this model, humans are seen as selfish, rational beings motivated through self-interest. They act to make things better for themselves, or, to use economic language, to maximize "utility function." This model has been criticized over the years for being too narrow. It doesn’t do a good job of explaining unselfish action, and it doesn't do a good job of explaining acts that make emotional sense but no economic sense.
"economic man" is the characterization of man in some economic theories as a rational person who pursues wealth for his own self-interest. The economic man is described as one who avoids unnecessary work by using rational judgment.